<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ddd5e-4561-791b-8109-aaef678b414e,g:fdc0fbe8-47e4-427a-9288-6e619a09aa67-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/Cover" xlink:type="simple" xlink:href="kzr-20260331.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019ddd5e-4627-7d89-bc4f-d7e510116e0b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_DocumentInformationTable_019ddd5e-4627-7d89-bc4f-d7e510116e0b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ddd5e-4627-781d-8324-52d916887ef9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019ddd5e-4627-7d89-bc4f-d7e510116e0b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ddd5e-4627-781d-8324-52d916887ef9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ddd5e-4627-781d-8324-52d916887ef9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ddd5e-4627-781d-8324-52d916887ef9" xlink:to="loc_us-gaap_ClassOfStockDomain_019ddd5e-4627-781d-8324-52d916887ef9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ddd5e-4627-7b84-8b4a-c2631eb469aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ddd5e-4627-781d-8324-52d916887ef9" xlink:to="loc_us-gaap_ClassOfStockDomain_019ddd5e-4627-7b84-8b4a-c2631eb469aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ddd5e-4627-7242-9042-022cba923438" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ddd5e-4627-7b84-8b4a-c2631eb469aa" xlink:to="loc_us-gaap_CommonStockMember_019ddd5e-4627-7242-9042-022cba923438" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_PreferredSharePurchaseRightMember_019ddd5e-4627-740b-9a4e-e61a9f5f63c1" xlink:href="kzr-20260331.xsd#kzr_PreferredSharePurchaseRightMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ddd5e-4627-7b84-8b4a-c2631eb469aa" xlink:to="loc_kzr_PreferredSharePurchaseRightMember_019ddd5e-4627-740b-9a4e-e61a9f5f63c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019ddd5e-4627-7ef3-a7bc-6acd29a3cba0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_DocumentType_019ddd5e-4627-7ef3-a7bc-6acd29a3cba0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019ddd5e-4627-75a8-a3ea-2289c522bfa1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_DocumentQuarterlyReport_019ddd5e-4627-75a8-a3ea-2289c522bfa1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019ddd5e-4627-76fd-b5f6-68b2d4d5b884" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_DocumentPeriodEndDate_019ddd5e-4627-76fd-b5f6-68b2d4d5b884" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019ddd5e-4627-75bf-9f19-c3b3ebc95618" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_DocumentTransitionReport_019ddd5e-4627-75bf-9f19-c3b3ebc95618" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019ddd5e-4627-78bc-bb3e-732d8d4f66cf" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityFileNumber_019ddd5e-4627-78bc-bb3e-732d8d4f66cf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019ddd5e-4627-7319-9621-09d1603c27dd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityRegistrantName_019ddd5e-4627-7319-9621-09d1603c27dd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019ddd5e-4627-78df-a8fd-70eb28b29e15" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019ddd5e-4627-78df-a8fd-70eb28b29e15" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019ddd5e-4627-79fb-999f-7e825be1a526" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityTaxIdentificationNumber_019ddd5e-4627-79fb-999f-7e825be1a526" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019ddd5e-4627-7123-9f7a-ce02063c8ac1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityAddressAddressLine1_019ddd5e-4627-7123-9f7a-ce02063c8ac1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019ddd5e-4627-771f-961e-f805cb709983" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityAddressAddressLine2_019ddd5e-4627-771f-961e-f805cb709983" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019ddd5e-4627-7bfd-9522-efcdf24a54e7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityAddressCityOrTown_019ddd5e-4627-7bfd-9522-efcdf24a54e7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019ddd5e-4627-7fe9-b8c7-2202c7fc08d5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityAddressStateOrProvince_019ddd5e-4627-7fe9-b8c7-2202c7fc08d5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019ddd5e-4627-787a-8767-6b7a767b21ab" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityAddressPostalZipCode_019ddd5e-4627-787a-8767-6b7a767b21ab" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019ddd5e-4627-7425-bb9f-49c53ff0f127" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_CityAreaCode_019ddd5e-4627-7425-bb9f-49c53ff0f127" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019ddd5e-4627-7883-9777-7a953aad6db9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_LocalPhoneNumber_019ddd5e-4627-7883-9777-7a953aad6db9" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019ddd5e-4627-7c23-930a-e5d9d0afdb44" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_Security12bTitle_019ddd5e-4627-7c23-930a-e5d9d0afdb44" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019ddd5e-4627-7a8c-9739-c6f8d5907d7d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_TradingSymbol_019ddd5e-4627-7a8c-9739-c6f8d5907d7d" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_NoTradingSymbolFlag_019ddd5e-4627-79ea-bd24-2092b3c03a4f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_NoTradingSymbolFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_NoTradingSymbolFlag_019ddd5e-4627-79ea-bd24-2092b3c03a4f" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019ddd5e-4627-7891-81df-5d1af756e123" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_SecurityExchangeName_019ddd5e-4627-7891-81df-5d1af756e123" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019ddd5e-4627-7d2f-b793-ec632834b664" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityCurrentReportingStatus_019ddd5e-4627-7d2f-b793-ec632834b664" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019ddd5e-4627-774b-93cb-177a1e920790" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityInteractiveDataCurrent_019ddd5e-4627-774b-93cb-177a1e920790" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019ddd5e-4627-77b7-8e2f-46c7bcfae4fd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityFilerCategory_019ddd5e-4627-77b7-8e2f-46c7bcfae4fd" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019ddd5e-4627-7441-af1c-3a9871a14c2a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntitySmallBusiness_019ddd5e-4627-7441-af1c-3a9871a14c2a" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019ddd5e-4627-770e-a73d-e2999b729800" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityEmergingGrowthCompany_019ddd5e-4627-770e-a73d-e2999b729800" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019ddd5e-4627-7af6-b24b-2075aca0ab9d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityShellCompany_019ddd5e-4627-7af6-b24b-2075aca0ab9d" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019ddd5e-4627-75ef-938b-f0da0e8d0e47" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019ddd5e-4627-75ef-938b-f0da0e8d0e47" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019ddd5e-4627-7847-b52d-2b16c424a04d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_EntityCentralIndexKey_019ddd5e-4627-7847-b52d-2b16c424a04d" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019ddd5e-4627-7892-b758-f57110492e62" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_CurrentFiscalYearEndDate_019ddd5e-4627-7892-b758-f57110492e62" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019ddd5e-4627-744e-861d-6ee10e742c6c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_AmendmentFlag_019ddd5e-4627-744e-861d-6ee10e742c6c" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019ddd5e-4627-7dcd-be0d-0d908114a00c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_DocumentFiscalYearFocus_019ddd5e-4627-7dcd-be0d-0d908114a00c" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019ddd5e-4627-7167-b634-d5812771c8e7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ddd5e-4627-7152-a450-14b131276a93" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019ddd5e-4627-7167-b634-d5812771c8e7" xlink:type="arc" order="30"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/CondensedConsolidatedStatementsofStockholdersEquityUnaudited" xlink:type="simple" xlink:href="kzr-20260331.xsd#CondensedConsolidatedStatementsofStockholdersEquityUnaudited"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/CondensedConsolidatedStatementsofStockholdersEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ddd5e-4627-7cce-b38b-7daedb5df314" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ddd5e-4627-7a56-a7f3-0fdbf99390d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ddd5e-4627-7cce-b38b-7daedb5df314" xlink:to="loc_us-gaap_StatementTable_019ddd5e-4627-7a56-a7f3-0fdbf99390d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ddd5e-4627-718f-8d5e-d59461f4ef13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ddd5e-4627-7a56-a7f3-0fdbf99390d1" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ddd5e-4627-718f-8d5e-d59461f4ef13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ddd5e-4627-718f-8d5e-d59461f4ef13_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ddd5e-4627-718f-8d5e-d59461f4ef13" xlink:to="loc_us-gaap_EquityComponentDomain_019ddd5e-4627-718f-8d5e-d59461f4ef13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ddd5e-4627-774d-9cdc-8746ece1356e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ddd5e-4627-718f-8d5e-d59461f4ef13" xlink:to="loc_us-gaap_EquityComponentDomain_019ddd5e-4627-774d-9cdc-8746ece1356e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ddd5e-4627-7109-903f-1ab21f00b2fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ddd5e-4627-774d-9cdc-8746ece1356e" xlink:to="loc_us-gaap_CommonStockMember_019ddd5e-4627-7109-903f-1ab21f00b2fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019ddd5e-4627-730d-aa28-c0f73564f9c4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ddd5e-4627-774d-9cdc-8746ece1356e" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019ddd5e-4627-730d-aa28-c0f73564f9c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ddd5e-4627-76d0-8935-b204b88cd46f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ddd5e-4627-774d-9cdc-8746ece1356e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ddd5e-4627-76d0-8935-b204b88cd46f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019ddd5e-4627-7f82-81ce-85150164970c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ddd5e-4627-774d-9cdc-8746ece1356e" xlink:to="loc_us-gaap_RetainedEarningsMember_019ddd5e-4627-7f82-81ce-85150164970c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ddd5e-4627-7cce-b38b-7daedb5df314" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ddd5e-4627-7a63-84e5-1b13f0db2ca2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ddd5e-4627-7a63-84e5-1b13f0db2ca2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ddd5e-4627-7219-94bb-adcc9497b403" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:to="loc_us-gaap_StockholdersEquity_019ddd5e-4627-7219-94bb-adcc9497b403" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_IssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansShares_019ddd5e-4627-74b1-9de9-82ee0827dd54" xlink:href="kzr-20260331.xsd#kzr_IssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:to="loc_kzr_IssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansShares_019ddd5e-4627-74b1-9de9-82ee0827dd54" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_IssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansValue_019ddd5e-4627-77df-a44f-0fcfbd70fc24" xlink:href="kzr-20260331.xsd#kzr_IssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:to="loc_kzr_IssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansValue_019ddd5e-4627-77df-a44f-0fcfbd70fc24" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ddd5e-4627-77f5-afdd-866d6b78c8c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ddd5e-4627-77f5-afdd-866d6b78c8c3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ddd5e-4627-7537-9465-e8dff65daedb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019ddd5e-4627-7537-9465-e8dff65daedb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ddd5e-4627-71e7-9f64-06ff6333d7a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019ddd5e-4627-7705-ab55-f311eac40b90" xlink:to="loc_us-gaap_NetIncomeLoss_019ddd5e-4627-71e7-9f64-06ff6333d7a9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ddd5e-4627-7c54-a96c-da7d288a7a52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ddd5e-4627-7dbc-a519-96db4b612bc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/OrganizationandDescriptionoftheBusinessDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#OrganizationandDescriptionoftheBusinessDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/OrganizationandDescriptionoftheBusinessDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:href="kzr-20260331.xsd#kzr_OrganizationAndDescriptionOfBusinessLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_OrganizationAndDescriptionOfBusinessTable_019ddd5e-4627-713a-a97a-61ee544e40f9" xlink:href="kzr-20260331.xsd#kzr_OrganizationAndDescriptionOfBusinessTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_kzr_OrganizationAndDescriptionOfBusinessTable_019ddd5e-4627-713a-a97a-61ee544e40f9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019ddd5e-4627-7c5a-8b48-f2a993917549" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessTable_019ddd5e-4627-713a-a97a-61ee544e40f9" xlink:to="loc_dei_LegalEntityAxis_019ddd5e-4627-7c5a-8b48-f2a993917549" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ddd5e-4627-7c5a-8b48-f2a993917549_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019ddd5e-4627-7c5a-8b48-f2a993917549" xlink:to="loc_dei_EntityDomain_019ddd5e-4627-7c5a-8b48-f2a993917549_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ddd5e-4627-71e2-a470-3b6898d6c0a6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019ddd5e-4627-7c5a-8b48-f2a993917549" xlink:to="loc_dei_EntityDomain_019ddd5e-4627-71e2-a470-3b6898d6c0a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_AuriniaPharmaU.S.Inc.Member_019ddd5e-4627-71f5-b94f-fbbe483bb401" xlink:href="kzr-20260331.xsd#kzr_AuriniaPharmaU.S.Inc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019ddd5e-4627-71e2-a470-3b6898d6c0a6" xlink:to="loc_kzr_AuriniaPharmaU.S.Inc.Member_019ddd5e-4627-71f5-b94f-fbbe483bb401" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019ddd5e-4627-78db-9100-b94f18339ec1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessTable_019ddd5e-4627-713a-a97a-61ee544e40f9" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019ddd5e-4627-78db-9100-b94f18339ec1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ddd5e-4627-78db-9100-b94f18339ec1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ddd5e-4627-78db-9100-b94f18339ec1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ddd5e-4627-78db-9100-b94f18339ec1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ddd5e-4627-7e6a-9d9d-d4820ed94abb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019ddd5e-4627-78db-9100-b94f18339ec1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ddd5e-4627-7e6a-9d9d-d4820ed94abb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_KezarLifeSciencesIncMember_019ddd5e-4627-786e-8249-1d663748d8fe" xlink:href="kzr-20260331.xsd#kzr_KezarLifeSciencesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019ddd5e-4627-7e6a-9d9d-d4820ed94abb" xlink:to="loc_kzr_KezarLifeSciencesIncMember_019ddd5e-4627-786e-8249-1d663748d8fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ddd5e-4627-7be3-9b87-d0f837592c31" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessTable_019ddd5e-4627-713a-a97a-61ee544e40f9" xlink:to="loc_srt_RangeAxis_019ddd5e-4627-7be3-9b87-d0f837592c31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ddd5e-4627-7be3-9b87-d0f837592c31_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ddd5e-4627-7be3-9b87-d0f837592c31" xlink:to="loc_srt_RangeMember_019ddd5e-4627-7be3-9b87-d0f837592c31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ddd5e-4627-76cb-8b96-7da0e8572bc4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ddd5e-4627-7be3-9b87-d0f837592c31" xlink:to="loc_srt_RangeMember_019ddd5e-4627-76cb-8b96-7da0e8572bc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ddd5e-4627-792a-9855-c4a087109538" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ddd5e-4627-76cb-8b96-7da0e8572bc4" xlink:to="loc_srt_MinimumMember_019ddd5e-4627-792a-9855-c4a087109538" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019ddd5e-4627-7e51-8721-71bcf7942d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019ddd5e-4627-7e51-8721-71bcf7942d1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ddd5e-4627-7a40-9bb8-8f0f7304545f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ddd5e-4627-7a40-9bb8-8f0f7304545f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionSharePrice_019ddd5e-4627-7e01-b136-34bc8977a331" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionSharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_us-gaap_BusinessAcquisitionSharePrice_019ddd5e-4627-7e01-b136-34bc8977a331" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_BusinessCombinationNumberOfContingentValueRight_019ddd5e-4627-722d-b8b9-ed1f9e2f5a4b" xlink:href="kzr-20260331.xsd#kzr_BusinessCombinationNumberOfContingentValueRight"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_kzr_BusinessCombinationNumberOfContingentValueRight_019ddd5e-4627-722d-b8b9-ed1f9e2f5a4b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfProductiveAssets_019ddd5e-4627-79e2-b671-69d7e7e924fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleOfProductiveAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_us-gaap_ProceedsFromSaleOfProductiveAssets_019ddd5e-4627-79e2-b671-69d7e7e924fe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_DevelopmentAndCommercialMilestoneAmountToBeReceived_019ddd5e-4627-7f16-80d5-bc94e39f2523" xlink:href="kzr-20260331.xsd#kzr_DevelopmentAndCommercialMilestoneAmountToBeReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_kzr_DevelopmentAndCommercialMilestoneAmountToBeReceived_019ddd5e-4627-7f16-80d5-bc94e39f2523" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019ddd5e-4627-7633-9a6f-2e5199ed3f95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019ddd5e-4627-7633-9a6f-2e5199ed3f95" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_SufficientCashAndCashEquivalentsAvailablePeriodTerm_019ddd5e-4627-7e44-bf0a-582ed20418ba" xlink:href="kzr-20260331.xsd#kzr_SufficientCashAndCashEquivalentsAvailablePeriodTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_kzr_SufficientCashAndCashEquivalentsAvailablePeriodTerm_019ddd5e-4627-7e44-bf0a-582ed20418ba" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_019ddd5e-4627-77c7-9778-7eb93e310472" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_019ddd5e-4627-77c7-9778-7eb93e310472" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_019de293-1d9c-71de-b196-f399dc051a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_us-gaap_RestructuringCharges_019de293-1d9c-71de-b196-f399dc051a8e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019e0257-08ae-7d0d-b5b1-774c0788a9b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostsAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_OrganizationAndDescriptionOfBusinessLineItems_019ddd5e-4627-7456-8bf3-3dee2afc0ea9" xlink:to="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019e0257-08ae-7d0d-b5b1-774c0788a9b8" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/FairValueMeasurementsDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#FairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/FairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ddd5e-4627-7172-9654-37da55b49df5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ddd5e-4627-7891-b05a-6aedc51fa4be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ddd5e-4627-7172-9654-37da55b49df5" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ddd5e-4627-7891-b05a-6aedc51fa4be" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ddd5e-4627-771c-8f40-eadd3525e8f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ddd5e-4627-7891-b05a-6aedc51fa4be" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ddd5e-4627-771c-8f40-eadd3525e8f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ddd5e-4627-771c-8f40-eadd3525e8f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ddd5e-4627-771c-8f40-eadd3525e8f4" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ddd5e-4627-771c-8f40-eadd3525e8f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ddd5e-4627-7220-863d-0b4d9a2514ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019ddd5e-4627-771c-8f40-eadd3525e8f4" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ddd5e-4627-7220-863d-0b4d9a2514ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019ddd5e-4627-7d8c-a02c-004c4739e0d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019ddd5e-4627-7220-863d-0b4d9a2514ac" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019ddd5e-4627-7d8c-a02c-004c4739e0d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ddd5e-4627-7fdb-bf94-b23818a49085" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ddd5e-4627-7891-b05a-6aedc51fa4be" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ddd5e-4627-7fdb-bf94-b23818a49085" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ddd5e-4627-7fdb-bf94-b23818a49085_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ddd5e-4627-7fdb-bf94-b23818a49085" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ddd5e-4627-7fdb-bf94-b23818a49085_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ddd5e-4627-709a-99ed-139f493b622e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ddd5e-4627-7fdb-bf94-b23818a49085" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ddd5e-4627-709a-99ed-139f493b622e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019ddd5e-4627-7b80-be8f-0b729196319d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ddd5e-4627-709a-99ed-139f493b622e" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019ddd5e-4627-7b80-be8f-0b729196319d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019ddd5e-4627-7387-ac05-e87e2d62cf60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ddd5e-4627-709a-99ed-139f493b622e" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019ddd5e-4627-7387-ac05-e87e2d62cf60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019ddd5e-4627-7a0d-a9c5-823df0a08b93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ddd5e-4627-709a-99ed-139f493b622e" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019ddd5e-4627-7a0d-a9c5-823df0a08b93" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019ddd5e-4627-730e-8f28-daf21f31137e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019ddd5e-4627-7891-b05a-6aedc51fa4be" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019ddd5e-4627-730e-8f28-daf21f31137e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ddd5e-4627-730e-8f28-daf21f31137e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019ddd5e-4627-730e-8f28-daf21f31137e" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ddd5e-4627-730e-8f28-daf21f31137e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ddd5e-4627-769c-8b6a-563dabfffa39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019ddd5e-4627-730e-8f28-daf21f31137e" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ddd5e-4627-769c-8b6a-563dabfffa39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019ddd5e-4627-7b4e-bb0f-d024b4912a35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ddd5e-4627-769c-8b6a-563dabfffa39" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019ddd5e-4627-7b4e-bb0f-d024b4912a35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019ddd5e-4627-71de-9a5d-249a554176c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ddd5e-4627-7172-9654-37da55b49df5" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019ddd5e-4627-71de-9a5d-249a554176c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019ddd5e-4627-7316-a99f-c9a005bd29d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019ddd5e-4627-7172-9654-37da55b49df5" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019ddd5e-4627-7316-a99f-c9a005bd29d6" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/BalanceSheetComponentsSummaryofPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#BalanceSheetComponentsSummaryofPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/BalanceSheetComponentsSummaryofPropertyandEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ddd5e-4628-7c9a-b625-4a570ef6d6be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ddd5e-4628-7b82-9b37-5fcb0bc04d9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ddd5e-4628-7c9a-b625-4a570ef6d6be" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ddd5e-4628-7b82-9b37-5fcb0bc04d9b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ddd5e-4628-701e-b014-917323879f12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019ddd5e-4628-7b82-9b37-5fcb0bc04d9b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ddd5e-4628-701e-b014-917323879f12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ddd5e-4628-701e-b014-917323879f12_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ddd5e-4628-701e-b014-917323879f12" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ddd5e-4628-701e-b014-917323879f12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ddd5e-4628-7943-9c7a-73f24ab4bf5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ddd5e-4628-701e-b014-917323879f12" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ddd5e-4628-7943-9c7a-73f24ab4bf5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019ddd5e-4628-7511-add6-6ab1512c9439" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ddd5e-4628-7943-9c7a-73f24ab4bf5f" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019ddd5e-4628-7511-add6-6ab1512c9439" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_019ddd5e-4628-798f-b78d-0053c1d15f0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ddd5e-4628-7943-9c7a-73f24ab4bf5f" xlink:to="loc_us-gaap_ComputerEquipmentMember_019ddd5e-4628-798f-b78d-0053c1d15f0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019ddd5e-4628-77ba-a5f3-20c91a0de5da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ddd5e-4628-7c9a-b625-4a570ef6d6be" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019ddd5e-4628-77ba-a5f3-20c91a0de5da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019ddd5e-4628-7331-858c-5a3fb7a91d8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ddd5e-4628-7c9a-b625-4a570ef6d6be" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019ddd5e-4628-7331-858c-5a3fb7a91d8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019ddd5e-4628-7398-8c2c-1d583b592aae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019ddd5e-4628-7c9a-b625-4a570ef6d6be" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019ddd5e-4628-7398-8c2c-1d583b592aae" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/LeaseAdditionalInformationDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#LeaseAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/LeaseAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_019ddd5e-4628-7b31-a187-468863411b27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_019ddd5e-4628-7b31-a187-468863411b27" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019ddd5e-4628-727b-aa20-62c3fe5dd678" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019ddd5e-4628-7b31-a187-468863411b27" xlink:to="loc_srt_StatementGeographicalAxis_019ddd5e-4628-727b-aa20-62c3fe5dd678" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ddd5e-4628-727b-aa20-62c3fe5dd678_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019ddd5e-4628-727b-aa20-62c3fe5dd678" xlink:to="loc_srt_SegmentGeographicalDomain_019ddd5e-4628-727b-aa20-62c3fe5dd678_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019ddd5e-4628-710d-a90d-b2a5171c825c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019ddd5e-4628-727b-aa20-62c3fe5dd678" xlink:to="loc_srt_SegmentGeographicalDomain_019ddd5e-4628-710d-a90d-b2a5171c825c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_SouthSanFranciscoCaliforniaMember_019ddd5e-4628-7100-b0bf-b937fe2fd292" xlink:href="kzr-20260331.xsd#kzr_SouthSanFranciscoCaliforniaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019ddd5e-4628-710d-a90d-b2a5171c825c" xlink:to="loc_kzr_SouthSanFranciscoCaliforniaMember_019ddd5e-4628-7100-b0bf-b937fe2fd292" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019ddd5e-4628-7892-8f23-8a82c7e90239" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_019ddd5e-4628-7b31-a187-468863411b27" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019ddd5e-4628-7892-8f23-8a82c7e90239" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-4628-7892-8f23-8a82c7e90239_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019ddd5e-4628-7892-8f23-8a82c7e90239" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-4628-7892-8f23-8a82c7e90239_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-4628-7d11-bb62-0695c691d47b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019ddd5e-4628-7892-8f23-8a82c7e90239" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-4628-7d11-bb62-0695c691d47b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019ddd5e-4628-7f55-bb23-139507619d02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-4628-7d11-bb62-0695c691d47b" xlink:to="loc_us-gaap_SubsequentEventMember_019ddd5e-4628-7f55-bb23-139507619d02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019e03e2-b1cf-72ae-991c-65ca66357c6e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019e03e2-b1cf-72ae-991c-65ca66357c6e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiability_019ddd5e-4628-7b1d-8452-a3398d8c12ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:to="loc_us-gaap_OperatingLeaseLiability_019ddd5e-4628-7b1d-8452-a3398d8c12ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseImpairmentLoss_019ddd5e-4628-704c-a4e5-322511141262" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:to="loc_us-gaap_OperatingLeaseImpairmentLoss_019ddd5e-4628-704c-a4e5-322511141262" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_EstimatedFutureSubleaseIncome_019ddd5e-4628-7b5d-9c7f-f437f8901530" xlink:href="kzr-20260331.xsd#kzr_EstimatedFutureSubleaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:to="loc_kzr_EstimatedFutureSubleaseIncome_019ddd5e-4628-7b5d-9c7f-f437f8901530" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_019e03ce-fff7-77c4-b385-4a62709487d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_019e03ce-fff7-77c4-b385-4a62709487d6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments_019ddd5e-4628-718b-a00d-9fcc59470ab0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:to="loc_us-gaap_OperatingLeasePayments_019ddd5e-4628-718b-a00d-9fcc59470ab0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_OperatingLeaseLiabilitySurrenderedSecurityDeposit_019e03cf-e44d-7b9a-8a0f-2d77922175ae" xlink:href="kzr-20260331.xsd#kzr_OperatingLeaseLiabilitySurrenderedSecurityDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_019ddd5e-4628-7b10-94b4-b13dbd5a6dbf" xlink:to="loc_kzr_OperatingLeaseLiabilitySurrenderedSecurityDeposit_019e03cf-e44d-7b9a-8a0f-2d77922175ae" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/StockholdersEquityDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#StockholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/StockholdersEquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_019ddd5e-4628-7ed9-b5b8-6deea69c1663" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_019ddd5e-4628-79be-aac2-1af2fbff5e4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019ddd5e-4628-7ed9-b5b8-6deea69c1663" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_019ddd5e-4628-79be-aac2-1af2fbff5e4c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_019ddd5e-4628-7e2a-89b7-ab0754d53a8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019ddd5e-4628-79be-aac2-1af2fbff5e4c" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_019ddd5e-4628-7e2a-89b7-ab0754d53a8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019ddd5e-4628-7e2a-89b7-ab0754d53a8b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019ddd5e-4628-7e2a-89b7-ab0754d53a8b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019ddd5e-4628-7e2a-89b7-ab0754d53a8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_019ddd5e-4628-7787-adaa-93429f4508a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_019ddd5e-4628-7e2a-89b7-ab0754d53a8b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_019ddd5e-4628-7787-adaa-93429f4508a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_StockholderRightsPlanMember_019ddd5e-4628-772e-af05-f301aad5d890" xlink:href="kzr-20260331.xsd#kzr_StockholderRightsPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019ddd5e-4628-7787-adaa-93429f4508a6" xlink:to="loc_kzr_StockholderRightsPlanMember_019ddd5e-4628-772e-af05-f301aad5d890" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_PassiveInstitutionalInvestorMember_019ddd5e-4628-7810-b5e8-59ec2a21d040" xlink:href="kzr-20260331.xsd#kzr_PassiveInstitutionalInvestorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_019ddd5e-4628-7787-adaa-93429f4508a6" xlink:to="loc_kzr_PassiveInstitutionalInvestorMember_019ddd5e-4628-7810-b5e8-59ec2a21d040" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ddd5e-4628-70da-a326-47fc76c15256" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_019ddd5e-4628-79be-aac2-1af2fbff5e4c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ddd5e-4628-70da-a326-47fc76c15256" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ddd5e-4628-70da-a326-47fc76c15256_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ddd5e-4628-70da-a326-47fc76c15256" xlink:to="loc_us-gaap_ClassOfStockDomain_019ddd5e-4628-70da-a326-47fc76c15256_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ddd5e-4628-7135-849a-7a00ca638d36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ddd5e-4628-70da-a326-47fc76c15256" xlink:to="loc_us-gaap_ClassOfStockDomain_019ddd5e-4628-7135-849a-7a00ca638d36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_SeriesAJuniorParticipatingPreferredStockMember_019ddd5e-4628-7952-8c6b-2096ed254f29" xlink:href="kzr-20260331.xsd#kzr_SeriesAJuniorParticipatingPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ddd5e-4628-7135-849a-7a00ca638d36" xlink:to="loc_kzr_SeriesAJuniorParticipatingPreferredStockMember_019ddd5e-4628-7952-8c6b-2096ed254f29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockDividendsShares_019ddd5e-4628-70be-a912-ac3d83e4f06e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockDividendsShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019ddd5e-4628-7ed9-b5b8-6deea69c1663" xlink:to="loc_us-gaap_PreferredStockDividendsShares_019ddd5e-4628-70be-a912-ac3d83e4f06e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_BeneficialOwnershipAcquiredPercentage_019ddd5e-4628-7f9f-866d-942adcecdde8" xlink:href="kzr-20260331.xsd#kzr_BeneficialOwnershipAcquiredPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019ddd5e-4628-7ed9-b5b8-6deea69c1663" xlink:to="loc_kzr_BeneficialOwnershipAcquiredPercentage_019ddd5e-4628-7f9f-866d-942adcecdde8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_PurchasePriceOfSharesUponRightsExercise_019ddd5e-4628-7bc4-8733-36ec5007db25" xlink:href="kzr-20260331.xsd#kzr_PurchasePriceOfSharesUponRightsExercise"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019ddd5e-4628-7ed9-b5b8-6deea69c1663" xlink:to="loc_kzr_PurchasePriceOfSharesUponRightsExercise_019ddd5e-4628-7bc4-8733-36ec5007db25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockConvertibleConversionRatio_019ddd5e-4628-7ecb-a3b0-c302377ea1e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockConvertibleConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019ddd5e-4628-7ed9-b5b8-6deea69c1663" xlink:to="loc_us-gaap_PreferredStockConvertibleConversionRatio_019ddd5e-4628-7ecb-a3b0-c302377ea1e0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ddd5e-4628-7ed3-a6ef-3a0868bfe55f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_019ddd5e-4628-7ed9-b5b8-6deea69c1663" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ddd5e-4628-7ed3-a6ef-3a0868bfe55f" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#StockBasedCompensationAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-4628-78fd-bbcb-672b11babf48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-4628-78fd-bbcb-672b11babf48" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019ddd5e-4628-7e33-a473-d4d8cdf0e4d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-4628-78fd-bbcb-672b11babf48" xlink:to="loc_us-gaap_PlanNameAxis_019ddd5e-4628-7e33-a473-d4d8cdf0e4d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7e33-a473-d4d8cdf0e4d6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019ddd5e-4628-7e33-a473-d4d8cdf0e4d6" xlink:to="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7e33-a473-d4d8cdf0e4d6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7c64-beb0-98bb719898ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019ddd5e-4628-7e33-a473-d4d8cdf0e4d6" xlink:to="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7c64-beb0-98bb719898ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_TwoThousandTwentyTwoStockIncentivePlanMember_019ddd5e-4628-7696-b77e-fc010548941a" xlink:href="kzr-20260331.xsd#kzr_TwoThousandTwentyTwoStockIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7c64-beb0-98bb719898ef" xlink:to="loc_kzr_TwoThousandTwentyTwoStockIncentivePlanMember_019ddd5e-4628-7696-b77e-fc010548941a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_TwoThousandEighteenEquityIncentivePlanMember_019ddd5e-4628-77ff-86e6-a7b168dd676e" xlink:href="kzr-20260331.xsd#kzr_TwoThousandEighteenEquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7c64-beb0-98bb719898ef" xlink:to="loc_kzr_TwoThousandEighteenEquityIncentivePlanMember_019ddd5e-4628-77ff-86e6-a7b168dd676e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_TwoThousandFifteenEquityIncentivePlanMember_019ddd5e-4628-74b0-8bf1-510c34a82c9f" xlink:href="kzr-20260331.xsd#kzr_TwoThousandFifteenEquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7c64-beb0-98bb719898ef" xlink:to="loc_kzr_TwoThousandFifteenEquityIncentivePlanMember_019ddd5e-4628-74b0-8bf1-510c34a82c9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_TwoThousandEighteenEmployeeStockPurchasePlanMember_019ddd5e-4628-75cd-b4b2-fc3d8c7d3295" xlink:href="kzr-20260331.xsd#kzr_TwoThousandEighteenEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7c64-beb0-98bb719898ef" xlink:to="loc_kzr_TwoThousandEighteenEmployeeStockPurchasePlanMember_019ddd5e-4628-75cd-b4b2-fc3d8c7d3295" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_TwoThousandEighteenPlanMember_019ddd5e-4628-7a0f-a190-c9bc5abf529b" xlink:href="kzr-20260331.xsd#kzr_TwoThousandEighteenPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019ddd5e-4628-7c64-beb0-98bb719898ef" xlink:to="loc_kzr_TwoThousandEighteenPlanMember_019ddd5e-4628-7a0f-a190-c9bc5abf529b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ddd5e-46ec-7865-978a-9610878b3ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-4628-78fd-bbcb-672b11babf48" xlink:to="loc_us-gaap_AwardTypeAxis_019ddd5e-46ec-7865-978a-9610878b3ec8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7865-978a-9610878b3ec8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ddd5e-46ec-7865-978a-9610878b3ec8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7865-978a-9610878b3ec8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7ac7-9ed3-eb991be59f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ddd5e-46ec-7865-978a-9610878b3ec8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7ac7-9ed3-eb991be59f5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ddd5e-46ec-79a0-b933-8ed24093767a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7ac7-9ed3-eb991be59f5f" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ddd5e-46ec-79a0-b933-8ed24093767a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_IncentiveStockOptionsMember_019ddd5e-46ec-7beb-9bc7-102ea3ec985e" xlink:href="kzr-20260331.xsd#kzr_IncentiveStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7ac7-9ed3-eb991be59f5f" xlink:to="loc_kzr_IncentiveStockOptionsMember_019ddd5e-46ec-7beb-9bc7-102ea3ec985e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_PerformanceBasedStockOptionsMember_019ddd5e-46ec-7dc6-af2f-c6239ecef108" xlink:href="kzr-20260331.xsd#kzr_PerformanceBasedStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7ac7-9ed3-eb991be59f5f" xlink:to="loc_kzr_PerformanceBasedStockOptionsMember_019ddd5e-46ec-7dc6-af2f-c6239ecef108" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ddd5e-46ec-7a25-9f51-0505e3637723" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7ac7-9ed3-eb991be59f5f" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ddd5e-46ec-7a25-9f51-0505e3637723" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019ddd5e-46ec-71ff-b35d-a90f8f8b83ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7ac7-9ed3-eb991be59f5f" xlink:to="loc_us-gaap_EmployeeStockMember_019ddd5e-46ec-71ff-b35d-a90f8f8b83ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ddd5e-46ec-7a54-a847-17ee228cd869" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-4628-78fd-bbcb-672b11babf48" xlink:to="loc_srt_RangeAxis_019ddd5e-46ec-7a54-a847-17ee228cd869" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ddd5e-46ec-7a54-a847-17ee228cd869_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ddd5e-46ec-7a54-a847-17ee228cd869" xlink:to="loc_srt_RangeMember_019ddd5e-46ec-7a54-a847-17ee228cd869_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ddd5e-46ec-7861-868c-33e1635a4a29" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ddd5e-46ec-7a54-a847-17ee228cd869" xlink:to="loc_srt_RangeMember_019ddd5e-46ec-7861-868c-33e1635a4a29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ddd5e-46ec-72a4-82b3-c300752398b7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ddd5e-46ec-7861-868c-33e1635a4a29" xlink:to="loc_srt_MaximumMember_019ddd5e-46ec-72a4-82b3-c300752398b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ddd5e-46ec-75bd-b530-1a49d21a8afb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-4628-78fd-bbcb-672b11babf48" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ddd5e-46ec-75bd-b530-1a49d21a8afb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ddd5e-46ec-75bd-b530-1a49d21a8afb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ddd5e-46ec-75bd-b530-1a49d21a8afb" xlink:to="loc_us-gaap_EquityComponentDomain_019ddd5e-46ec-75bd-b530-1a49d21a8afb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ddd5e-46ec-7ed8-8d31-5ba7bc643284" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ddd5e-46ec-75bd-b530-1a49d21a8afb" xlink:to="loc_us-gaap_EquityComponentDomain_019ddd5e-46ec-7ed8-8d31-5ba7bc643284" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ddd5e-46ec-7c56-849e-1bf74ef4ec24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ddd5e-46ec-7ed8-8d31-5ba7bc643284" xlink:to="loc_us-gaap_CommonStockMember_019ddd5e-46ec-7c56-849e-1bf74ef4ec24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019ddd5e-46ec-7079-8bbd-5f1fb4fa0033" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-4628-78fd-bbcb-672b11babf48" xlink:to="loc_us-gaap_VestingAxis_019ddd5e-46ec-7079-8bbd-5f1fb4fa0033" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019ddd5e-46ec-7079-8bbd-5f1fb4fa0033_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019ddd5e-46ec-7079-8bbd-5f1fb4fa0033" xlink:to="loc_us-gaap_VestingDomain_019ddd5e-46ec-7079-8bbd-5f1fb4fa0033_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019ddd5e-46ec-7e8b-92fe-72ba885c3433" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019ddd5e-46ec-7079-8bbd-5f1fb4fa0033" xlink:to="loc_us-gaap_VestingDomain_019ddd5e-46ec-7e8b-92fe-72ba885c3433" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019ddd5e-46ec-7c1c-9050-277bc7f3eab6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019ddd5e-46ec-7e8b-92fe-72ba885c3433" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019ddd5e-46ec-7c1c-9050-277bc7f3eab6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019ddd5e-46ec-75a2-aeef-f0bf19df17e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019ddd5e-46ec-7e8b-92fe-72ba885c3433" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019ddd5e-46ec-75a2-aeef-f0bf19df17e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019ddd5e-46ec-7a1f-b3e6-0e91066bcaad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019ddd5e-46ec-7e8b-92fe-72ba885c3433" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_019ddd5e-46ec-7a1f-b3e6-0e91066bcaad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019ddd5e-46ec-7131-8dfb-30377b38fb5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019ddd5e-46ec-7131-8dfb-30377b38fb5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019ddd5e-46ec-7232-9124-ec5519e1e537" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019ddd5e-46ec-7232-9124-ec5519e1e537" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019ddd5e-46ec-79c1-a35a-76fa77364839" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019ddd5e-46ec-79c1-a35a-76fa77364839" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019ddd5e-46ec-75d4-a075-aa9ee40bfc67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019ddd5e-46ec-75d4-a075-aa9ee40bfc67" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesIncreaseAutomaticallyThroughEveryYearOnSpecifiedDate_019ddd5e-46ec-74d3-87da-a186a784321a" xlink:href="kzr-20260331.xsd#kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesIncreaseAutomaticallyThroughEveryYearOnSpecifiedDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesIncreaseAutomaticallyThroughEveryYearOnSpecifiedDate_019ddd5e-46ec-74d3-87da-a186a784321a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_IncreaseInNumberOfSharesReservedForIssuanceAsPercentageOfTotalNumberOfSharesOfCapitalStockOutstandingOnLastDateOfPrecedingCalendarYear_019ddd5e-46ec-7246-97fa-39c58113cca5" xlink:href="kzr-20260331.xsd#kzr_IncreaseInNumberOfSharesReservedForIssuanceAsPercentageOfTotalNumberOfSharesOfCapitalStockOutstandingOnLastDateOfPrecedingCalendarYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_IncreaseInNumberOfSharesReservedForIssuanceAsPercentageOfTotalNumberOfSharesOfCapitalStockOutstandingOnLastDateOfPrecedingCalendarYear_019ddd5e-46ec-7246-97fa-39c58113cca5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019ddd5e-46ec-7857-a249-18b83f86eaf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019ddd5e-46ec-7857-a249-18b83f86eaf3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019ddd5e-46ec-79af-9303-425474960305" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019ddd5e-46ec-79af-9303-425474960305" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019ddd5e-46ec-76ce-9d6c-83774c1e82cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019ddd5e-46ec-76ce-9d6c-83774c1e82cc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_OptionsToPurchaseOfCommonStockOutstanding_019ddd5e-46ec-7491-b630-c3e4e9ba0783" xlink:href="kzr-20260331.xsd#kzr_OptionsToPurchaseOfCommonStockOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_OptionsToPurchaseOfCommonStockOutstanding_019ddd5e-46ec-7491-b630-c3e4e9ba0783" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInNumberOfCommonStockSharesPercent_019ddd5e-46ec-7fb3-bde5-4bcf87002c40" xlink:href="kzr-20260331.xsd#kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInNumberOfCommonStockSharesPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInNumberOfCommonStockSharesPercent_019ddd5e-46ec-7fb3-bde5-4bcf87002c40" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInNumberOfCommonStockShares_019ddd5e-46ec-781b-b15c-fbbef68ebba6" xlink:href="kzr-20260331.xsd#kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInNumberOfCommonStockShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInNumberOfCommonStockShares_019ddd5e-46ec-781b-b15c-fbbef68ebba6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_CommonStockAdditionalSharesAuthorizedForFutureIssuance_019ddd5e-46ec-7ffa-b7cb-b6ad01b630ad" xlink:href="kzr-20260331.xsd#kzr_CommonStockAdditionalSharesAuthorizedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_CommonStockAdditionalSharesAuthorizedForFutureIssuance_019ddd5e-46ec-7ffa-b7cb-b6ad01b630ad" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019ddd5e-46ec-7246-81b8-e85f3f74d2b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_CommonStockSharesIssued_019ddd5e-46ec-7246-81b8-e85f3f74d2b2" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019ddd5e-46ec-7924-ba23-d8ede4490c99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019ddd5e-46ec-7924-ba23-d8ede4490c99" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ShareBasedPaymentArrangementOptionExercisePriceRangeOutstandingModifiedExercisePrice_019ddd5e-46ec-749d-a0b9-e7ba61bbc79f" xlink:href="kzr-20260331.xsd#kzr_ShareBasedPaymentArrangementOptionExercisePriceRangeOutstandingModifiedExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_ShareBasedPaymentArrangementOptionExercisePriceRangeOutstandingModifiedExercisePrice_019ddd5e-46ec-749d-a0b9-e7ba61bbc79f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost_019ddd5e-46ec-7a0a-92df-b0baedd1c87a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost_019ddd5e-46ec-7a0a-92df-b0baedd1c87a" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ShareBasedCompensationExpensePlanModificationUnamortizedIncrementalCompensationCostOfUnvestedOptionShares_019ddd5e-46ec-7d16-914d-6ca535513df6" xlink:href="kzr-20260331.xsd#kzr_ShareBasedCompensationExpensePlanModificationUnamortizedIncrementalCompensationCostOfUnvestedOptionShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_ShareBasedCompensationExpensePlanModificationUnamortizedIncrementalCompensationCostOfUnvestedOptionShares_019ddd5e-46ec-7d16-914d-6ca535513df6" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019de29e-7790-7c44-bbee-1aea8f36242f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019de29e-7790-7c44-bbee-1aea8f36242f" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_019de2a0-8b04-72a3-ba92-0ef2d12bf5fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_019de2a0-8b04-72a3-ba92-0ef2d12bf5fd" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_019ddd5e-46ec-751b-b452-f33e847cecb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeBenefitsAndShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_EmployeeBenefitsAndShareBasedCompensation_019ddd5e-46ec-751b-b452-f33e847cecb0" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ddd5e-46ec-7635-b354-e80506d3c624" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ddd5e-46ec-7635-b354-e80506d3c624" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019ddd5e-46ec-7953-85dd-d424156add0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019ddd5e-46ec-7953-85dd-d424156add0b" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019ddd5e-46ec-79f0-b1b7-97b9cdf98b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019ddd5e-46ec-79f0-b1b7-97b9cdf98b7c" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019ddd5e-46ec-772b-ae29-c1e1544ad9cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019ddd5e-46ec-772b-ae29-c1e1544ad9cd" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardLookBackPeriod_019ddd5e-46ec-76cc-b386-729d7705c2de" xlink:href="kzr-20260331.xsd#kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardLookBackPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_kzr_ShareBasedCompensationArrangementByShareBasedPaymentAwardLookBackPeriod_019ddd5e-46ec-76cc-b386-729d7705c2de" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_019ddd5e-46ec-7710-85c0-a41807f1d0e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_019ddd5e-46ec-7710-85c0-a41807f1d0e1" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019ddd5e-46ec-77f2-b7a9-b5465dbe3bec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-72fe-ad05-403fd08329b8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019ddd5e-46ec-77f2-b7a9-b5465dbe3bec" xlink:type="arc" order="27"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/StockBasedCompensationSummaryofRSUActivityDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#StockBasedCompensationSummaryofRSUActivityDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/StockBasedCompensationSummaryofRSUActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-7368-a429-5f7a88eab26b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-46ec-78c4-8246-5fb35761a3e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-7368-a429-5f7a88eab26b" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-46ec-78c4-8246-5fb35761a3e2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ddd5e-46ec-7666-b6b0-95a52cbe4430" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-46ec-78c4-8246-5fb35761a3e2" xlink:to="loc_us-gaap_AwardTypeAxis_019ddd5e-46ec-7666-b6b0-95a52cbe4430" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7666-b6b0-95a52cbe4430_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ddd5e-46ec-7666-b6b0-95a52cbe4430" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-7666-b6b0-95a52cbe4430_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-73a4-ac17-941a79ff050d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ddd5e-46ec-7666-b6b0-95a52cbe4430" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-73a4-ac17-941a79ff050d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ddd5e-46ec-7b5c-8bf5-2fa123b65fb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ddd5e-46ec-73a4-ac17-941a79ff050d" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ddd5e-46ec-7b5c-8bf5-2fa123b65fb2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019ddd5e-46ec-7a9c-b36f-ff27684e2394" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-46ec-78c4-8246-5fb35761a3e2" xlink:to="loc_us-gaap_PlanNameAxis_019ddd5e-46ec-7a9c-b36f-ff27684e2394" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019ddd5e-46ec-7a9c-b36f-ff27684e2394_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019ddd5e-46ec-7a9c-b36f-ff27684e2394" xlink:to="loc_us-gaap_PlanNameDomain_019ddd5e-46ec-7a9c-b36f-ff27684e2394_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019ddd5e-46ec-7033-91e8-23b0ac90086d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019ddd5e-46ec-7a9c-b36f-ff27684e2394" xlink:to="loc_us-gaap_PlanNameDomain_019ddd5e-46ec-7033-91e8-23b0ac90086d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_TwoThousandEighteenEquityIncentivePlanMember_019ddd5e-46ec-7b65-9875-14b19a7636f1" xlink:href="kzr-20260331.xsd#kzr_TwoThousandEighteenEquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019ddd5e-46ec-7033-91e8-23b0ac90086d" xlink:to="loc_kzr_TwoThousandEighteenEquityIncentivePlanMember_019ddd5e-46ec-7b65-9875-14b19a7636f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ddd5e-46ec-7669-8136-0e72ba0f0d3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-7368-a429-5f7a88eab26b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ddd5e-46ec-7669-8136-0e72ba0f0d3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ddd5e-46ec-7df6-b713-354e91cb44ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ddd5e-46ec-7669-8136-0e72ba0f0d3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ddd5e-46ec-7df6-b713-354e91cb44ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019ddd5e-46ec-7aab-9a8d-51d0f9a7a680" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ddd5e-46ec-7669-8136-0e72ba0f0d3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019ddd5e-46ec-7aab-9a8d-51d0f9a7a680" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019ddd5e-46ec-752e-acf5-a3bd6451859a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ddd5e-46ec-7a51-bc9e-2bffe2cfbfad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-7368-a429-5f7a88eab26b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ddd5e-46ec-7a51-bc9e-2bffe2cfbfad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ddd5e-46ec-713a-bca5-abb489c61a54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ddd5e-46ec-7a51-bc9e-2bffe2cfbfad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ddd5e-46ec-713a-bca5-abb489c61a54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019ddd5e-46ec-7189-b307-11857372481c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019ddd5e-46ec-7a51-bc9e-2bffe2cfbfad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019ddd5e-46ec-7189-b307-11857372481c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019ddd5e-46ec-777f-9879-872c41cbe015" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/StockBasedCompensationSummaryofStockBasedCompensationExpenseRecognizedDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#StockBasedCompensationSummaryofStockBasedCompensationExpenseRecognizedDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/StockBasedCompensationSummaryofStockBasedCompensationExpenseRecognizedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ddd5e-46ec-7cb2-b748-18953f7a3b97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019ddd5e-46ec-7914-9b0e-54d4bc5b596d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ddd5e-46ec-7cb2-b748-18953f7a3b97" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019ddd5e-46ec-7914-9b0e-54d4bc5b596d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019de2a8-0352-72f2-93ec-e8dcea640dc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019ddd5e-46ec-7914-9b0e-54d4bc5b596d" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019de2a8-0352-72f2-93ec-e8dcea640dc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ddd5e-46ec-777e-a309-5301c98746fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ddd5e-46ec-7cb2-b748-18953f7a3b97" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ddd5e-46ec-777e-a309-5301c98746fe" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/StockBasedCompensationSummaryofStockBasedCompensationExpenseRecognizedDetails_1" xlink:type="simple" xlink:href="kzr-20260331.xsd#StockBasedCompensationSummaryofStockBasedCompensationExpenseRecognizedDetails_1"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/StockBasedCompensationSummaryofStockBasedCompensationExpenseRecognizedDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ddd5e-46ec-7cb2-b748-18953f7a3b97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019ddd5e-46ec-7914-9b0e-54d4bc5b596d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ddd5e-46ec-7cb2-b748-18953f7a3b97" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019ddd5e-46ec-7914-9b0e-54d4bc5b596d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ddd5e-46ec-777e-a309-5301c98746fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019ddd5e-46ec-7cb2-b748-18953f7a3b97" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019ddd5e-46ec-777e-a309-5301c98746fe" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/StockBasedCompensationSummaryofFairValueofEmployeeStockOptionsGrantedisCalculatedUsingBlackScholesOptionPricingModelwithRangeofAssumptionsDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#StockBasedCompensationSummaryofFairValueofEmployeeStockOptionsGrantedisCalculatedUsingBlackScholesOptionPricingModelwithRangeofAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/StockBasedCompensationSummaryofFairValueofEmployeeStockOptionsGrantedisCalculatedUsingBlackScholesOptionPricingModelwithRangeofAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-46ec-71c6-bcbc-7dff3c7feb47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-46ec-71c6-bcbc-7dff3c7feb47" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ddd5e-46ec-7f73-836b-01e6263e09fb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ddd5e-46ec-71c6-bcbc-7dff3c7feb47" xlink:to="loc_srt_RangeAxis_019ddd5e-46ec-7f73-836b-01e6263e09fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ddd5e-46ec-7f73-836b-01e6263e09fb_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ddd5e-46ec-7f73-836b-01e6263e09fb" xlink:to="loc_srt_RangeMember_019ddd5e-46ec-7f73-836b-01e6263e09fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ddd5e-46ec-7a52-aafe-6f3495d766db" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ddd5e-46ec-7f73-836b-01e6263e09fb" xlink:to="loc_srt_RangeMember_019ddd5e-46ec-7a52-aafe-6f3495d766db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ddd5e-46ec-733d-adc2-26f68a9a40bd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ddd5e-46ec-7a52-aafe-6f3495d766db" xlink:to="loc_srt_MinimumMember_019ddd5e-46ec-733d-adc2-26f68a9a40bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ddd5e-46ec-7e92-bbb6-a8c8f7e10d41" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ddd5e-46ec-7a52-aafe-6f3495d766db" xlink:to="loc_srt_MaximumMember_019ddd5e-46ec-7e92-bbb6-a8c8f7e10d41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019ddd5e-46ec-7a5e-8370-e5ac430a0c41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019ddd5e-46ec-7a5e-8370-e5ac430a0c41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019df442-d3dd-7fc5-ac68-9d7cbdf1340c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019df442-d3dd-7fc5-ac68-9d7cbdf1340c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_019ddd5e-46ec-7485-94d4-2b9874e6e840" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_019ddd5e-46ec-7485-94d4-2b9874e6e840" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_019ddd5e-46ec-753e-a98c-b7dc56181983" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_019ddd5e-46ec-753e-a98c-b7dc56181983" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019df448-ee5c-70f8-afa7-3ef2c367af05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019df448-ee5c-70f8-afa7-3ef2c367af05" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_019ddd5e-46ec-74b5-99d0-9ea1fcb0af1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_019ddd5e-46ec-74b5-99d0-9ea1fcb0af1e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_019ddd5e-46ec-70bf-b0fe-ade6608ee8b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_019ddd5e-46ec-70bf-b0fe-ade6608ee8b5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019ddd5e-46ec-7634-9740-8ce649a442ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ddd5e-46ec-78b3-bc38-97227410f731" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019ddd5e-46ec-7634-9740-8ce649a442ba" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/EverestCollaborationDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#EverestCollaborationDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/EverestCollaborationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ddd5e-46ec-780f-bce9-9c7713bbc681" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ddd5e-46ec-7830-be6e-d12166049fd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ddd5e-46ec-780f-bce9-9c7713bbc681" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ddd5e-46ec-7830-be6e-d12166049fd5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019ddd5e-46ec-7bdd-a682-efb1d622ff59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ddd5e-46ec-7830-be6e-d12166049fd5" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019ddd5e-46ec-7bdd-a682-efb1d622ff59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ddd5e-46ec-7bdd-a682-efb1d622ff59_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ddd5e-46ec-7bdd-a682-efb1d622ff59" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ddd5e-46ec-7bdd-a682-efb1d622ff59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ddd5e-46ec-716e-ad6a-5c3ecfdc777d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019ddd5e-46ec-7bdd-a682-efb1d622ff59" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ddd5e-46ec-716e-ad6a-5c3ecfdc777d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_EverestLicenseAgreementMember_019ddd5e-46ec-7cb5-8910-6105856d750b" xlink:href="kzr-20260331.xsd#kzr_EverestLicenseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019ddd5e-46ec-716e-ad6a-5c3ecfdc777d" xlink:to="loc_kzr_EverestLicenseAgreementMember_019ddd5e-46ec-7cb5-8910-6105856d750b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ddd5e-46ec-7663-ae23-b9a301bb55ac" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_019ddd5e-46ec-7830-be6e-d12166049fd5" xlink:to="loc_srt_ProductOrServiceAxis_019ddd5e-46ec-7663-ae23-b9a301bb55ac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7663-ae23-b9a301bb55ac_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ddd5e-46ec-7663-ae23-b9a301bb55ac" xlink:to="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7663-ae23-b9a301bb55ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7d86-a081-bf8c435ea9d1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ddd5e-46ec-7663-ae23-b9a301bb55ac" xlink:to="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7d86-a081-bf8c435ea9d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_CollaborationRevenueMember_019ddd5e-46ec-71a9-83a6-ffbaf5fcbaaa" xlink:href="kzr-20260331.xsd#kzr_CollaborationRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7d86-a081-bf8c435ea9d1" xlink:to="loc_kzr_CollaborationRevenueMember_019ddd5e-46ec-71a9-83a6-ffbaf5fcbaaa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_DevelopmentRegulatoryAndCommercialMilestonesMember_019ddd5e-46ec-70e4-8876-b4ba526d37fe" xlink:href="kzr-20260331.xsd#kzr_DevelopmentRegulatoryAndCommercialMilestonesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7d86-a081-bf8c435ea9d1" xlink:to="loc_kzr_DevelopmentRegulatoryAndCommercialMilestonesMember_019ddd5e-46ec-70e4-8876-b4ba526d37fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_019ddd5e-46ec-7778-b4d5-2920389208e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7d86-a081-bf8c435ea9d1" xlink:to="loc_us-gaap_RoyaltyMember_019ddd5e-46ec-7778-b4d5-2920389208e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_CollaborativeAgreementUpfrontPaymentsCollected_019ddd5e-46ec-7c57-af27-6c6d1d25b24c" xlink:href="kzr-20260331.xsd#kzr_CollaborativeAgreementUpfrontPaymentsCollected"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ddd5e-46ec-780f-bce9-9c7713bbc681" xlink:to="loc_kzr_CollaborativeAgreementUpfrontPaymentsCollected_019ddd5e-46ec-7c57-af27-6c6d1d25b24c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_AdditionalPaymentsReceivableOnMilestoneAchievements_019ddd5e-46ec-7c78-848e-ff6112240c49" xlink:href="kzr-20260331.xsd#kzr_AdditionalPaymentsReceivableOnMilestoneAchievements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ddd5e-46ec-780f-bce9-9c7713bbc681" xlink:to="loc_kzr_AdditionalPaymentsReceivableOnMilestoneAchievements_019ddd5e-46ec-7c78-848e-ff6112240c49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019ddd5e-46ec-73d4-b56d-d73498f93942" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ddd5e-46ec-780f-bce9-9c7713bbc681" xlink:to="loc_us-gaap_Revenues_019ddd5e-46ec-73d4-b56d-d73498f93942" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_NoncurrentUnbilledReceivableFromCollaboration_019de2ae-b64f-7c35-8e98-d5e3b12c2358" xlink:href="kzr-20260331.xsd#kzr_NoncurrentUnbilledReceivableFromCollaboration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ddd5e-46ec-780f-bce9-9c7713bbc681" xlink:to="loc_kzr_NoncurrentUnbilledReceivableFromCollaboration_019de2ae-b64f-7c35-8e98-d5e3b12c2358" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ContraResearchAndDevelopmentExpense_019ddd5e-46ec-762a-941a-e1ccd3168614" xlink:href="kzr-20260331.xsd#kzr_ContraResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_019ddd5e-46ec-780f-bce9-9c7713bbc681" xlink:to="loc_kzr_ContraResearchAndDevelopmentExpense_019ddd5e-46ec-762a-941a-e1ccd3168614" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/NetLossPerShareSummaryofAntidilutiveOutstandingSharesofCommonStockEquivalentsExcludedfromComputationofDilutedNetLossperShareDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#NetLossPerShareSummaryofAntidilutiveOutstandingSharesofCommonStockEquivalentsExcludedfromComputationofDilutedNetLossperShareDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/NetLossPerShareSummaryofAntidilutiveOutstandingSharesofCommonStockEquivalentsExcludedfromComputationofDilutedNetLossperShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ddd5e-46ec-74d6-9a37-ecba8b298edc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ddd5e-46ec-7012-85b1-498ed5ba3b78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ddd5e-46ec-74d6-9a37-ecba8b298edc" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ddd5e-46ec-7012-85b1-498ed5ba3b78" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ddd5e-46ec-74c5-a33d-0748ce3baa16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019ddd5e-46ec-7012-85b1-498ed5ba3b78" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ddd5e-46ec-74c5-a33d-0748ce3baa16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ddd5e-46ec-74c5-a33d-0748ce3baa16_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ddd5e-46ec-74c5-a33d-0748ce3baa16" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ddd5e-46ec-74c5-a33d-0748ce3baa16_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ddd5e-46ec-7f42-8078-c59c81f83986" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019ddd5e-46ec-74c5-a33d-0748ce3baa16" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ddd5e-46ec-7f42-8078-c59c81f83986" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ddd5e-46ec-78d2-97da-0baf5ebd0c3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ddd5e-46ec-7f42-8078-c59c81f83986" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ddd5e-46ec-78d2-97da-0baf5ebd0c3b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_RestrictedStockUnitsSubjectToFutureVestingMember_019ddd5e-46ec-7109-9bf2-3162e22f3b32" xlink:href="kzr-20260331.xsd#kzr_RestrictedStockUnitsSubjectToFutureVestingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019ddd5e-46ec-7f42-8078-c59c81f83986" xlink:to="loc_kzr_RestrictedStockUnitsSubjectToFutureVestingMember_019ddd5e-46ec-7109-9bf2-3162e22f3b32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019ddd5e-46ec-7912-b036-d95897cbab28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019ddd5e-46ec-74d6-9a37-ecba8b298edc" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019ddd5e-46ec-7912-b036-d95897cbab28" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/RestructuringandImpairmentChargesAdditionalInformationDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#RestructuringandImpairmentChargesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/RestructuringandImpairmentChargesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019de2be-2c68-754b-8d22-2806ca8056df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019de2be-2c68-7ad0-9f17-c3a37fd3456c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019de2be-2c68-754b-8d22-2806ca8056df" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019de2be-2c68-7ad0-9f17-c3a37fd3456c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019de2be-2c68-7dc8-b0f9-d24130009379" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019de2be-2c68-7ad0-9f17-c3a37fd3456c" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019de2be-2c68-7dc8-b0f9-d24130009379" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019de2be-2c68-7dc8-b0f9-d24130009379_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019de2be-2c68-7dc8-b0f9-d24130009379" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019de2be-2c68-7dc8-b0f9-d24130009379_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019de2be-2c68-7c0d-9be7-6ab243dbab19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019de2be-2c68-7dc8-b0f9-d24130009379" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019de2be-2c68-7c0d-9be7-6ab243dbab19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_019de2be-2c68-7cf0-8be1-98f6e9585f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019de2be-2c68-7c0d-9be7-6ab243dbab19" xlink:to="loc_us-gaap_EmployeeSeveranceMember_019de2be-2c68-7cf0-8be1-98f6e9585f5f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_019ddd5e-46ec-7204-b2d0-2700ffaeee08" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019de2be-2c68-754b-8d22-2806ca8056df" xlink:to="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_019ddd5e-46ec-7204-b2d0-2700ffaeee08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019de2be-2c68-72ba-86c1-1a0152f1cbcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostsAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019de2be-2c68-754b-8d22-2806ca8056df" xlink:to="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019de2be-2c68-72ba-86c1-1a0152f1cbcd" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/RestructuringandImpairmentChargesSummaryofAccrualActivityandPaymentsRelatingtoRestructuringandImpairmentChargeDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#RestructuringandImpairmentChargesSummaryofAccrualActivityandPaymentsRelatingtoRestructuringandImpairmentChargeDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/RestructuringandImpairmentChargesSummaryofAccrualActivityandPaymentsRelatingtoRestructuringandImpairmentChargeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019ddd5e-46ec-70ce-94cf-1e616e33de1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ddd5e-46ec-75b6-9217-3c4f3bdd0d61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ddd5e-46ec-70ce-94cf-1e616e33de1d" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ddd5e-46ec-75b6-9217-3c4f3bdd0d61" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019ddd5e-46ec-7964-abaa-a293e3692ef1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019ddd5e-46ec-75b6-9217-3c4f3bdd0d61" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019ddd5e-46ec-7964-abaa-a293e3692ef1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019ddd5e-46ec-7964-abaa-a293e3692ef1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019ddd5e-46ec-7964-abaa-a293e3692ef1" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019ddd5e-46ec-7964-abaa-a293e3692ef1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019ddd5e-46ec-7ec5-8e87-6b14dbcf167d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019ddd5e-46ec-7964-abaa-a293e3692ef1" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019ddd5e-46ec-7ec5-8e87-6b14dbcf167d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_019ddd5e-46ec-7a66-8553-0071b18121b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019ddd5e-46ec-7ec5-8e87-6b14dbcf167d" xlink:to="loc_us-gaap_EmployeeSeveranceMember_019ddd5e-46ec-7a66-8553-0071b18121b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_AssetImpairmentsMember_019ddd5e-46ec-7efe-b894-dbfa1d7add3a" xlink:href="kzr-20260331.xsd#kzr_AssetImpairmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019ddd5e-46ec-7ec5-8e87-6b14dbcf167d" xlink:to="loc_kzr_AssetImpairmentsMember_019ddd5e-46ec-7efe-b894-dbfa1d7add3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_019ddd5e-46ec-7f1d-98e3-45ab7810240a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019ddd5e-46ec-70ce-94cf-1e616e33de1d" xlink:to="loc_us-gaap_RestructuringReserveRollForward_019ddd5e-46ec-7f1d-98e3-45ab7810240a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_019ddd5e-46ec-7a09-bdb9-e733f12e6b4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019ddd5e-46ec-7f1d-98e3-45ab7810240a" xlink:to="loc_us-gaap_RestructuringReserve_019ddd5e-46ec-7a09-bdb9-e733f12e6b4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_019ddd5e-46ec-7f8e-8d33-596b2505dc6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019ddd5e-46ec-7f1d-98e3-45ab7810240a" xlink:to="loc_us-gaap_RestructuringCharges_019ddd5e-46ec-7f8e-8d33-596b2505dc6b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_019ddd5e-46ec-77d3-9014-232fa3f9b208" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019ddd5e-46ec-7f1d-98e3-45ab7810240a" xlink:to="loc_us-gaap_PaymentsForRestructuring_019ddd5e-46ec-77d3-9014-232fa3f9b208" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveSettledWithoutCash2_019ddd5e-46ec-77c2-91a9-3b9ab4191d19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringReserveSettledWithoutCash2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019ddd5e-46ec-7f1d-98e3-45ab7810240a" xlink:to="loc_us-gaap_RestructuringReserveSettledWithoutCash2_019ddd5e-46ec-77c2-91a9-3b9ab4191d19" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_019ddd5e-46ec-77c0-af8e-5e8ab1f36521" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringReserve"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/SegmentReportingSummaryofFinancialInformationforSegmentDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#SegmentReportingSummaryofFinancialInformationforSegmentDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/SegmentReportingSummaryofFinancialInformationforSegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ddd5e-46ec-77d9-abf8-ddaa0c3c5910" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ddd5e-46ec-77d9-abf8-ddaa0c3c5910" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019ddd5e-46ec-7c1a-ab21-f180034bf07f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ddd5e-46ec-77d9-abf8-ddaa0c3c5910" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019ddd5e-46ec-7c1a-ab21-f180034bf07f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ddd5e-46ec-7c1a-ab21-f180034bf07f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ddd5e-46ec-7c1a-ab21-f180034bf07f" xlink:to="loc_us-gaap_SegmentDomain_019ddd5e-46ec-7c1a-ab21-f180034bf07f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019ddd5e-46ec-76d2-84e1-74ad9ef336b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019ddd5e-46ec-7c1a-ab21-f180034bf07f" xlink:to="loc_us-gaap_SegmentDomain_019ddd5e-46ec-76d2-84e1-74ad9ef336b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ReportableSegmentMember_019ddd5e-46ec-72fa-8278-4f374abd60a6" xlink:href="kzr-20260331.xsd#kzr_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019ddd5e-46ec-76d2-84e1-74ad9ef336b8" xlink:to="loc_kzr_ReportableSegmentMember_019ddd5e-46ec-72fa-8278-4f374abd60a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ddd5e-46ec-7209-8587-56d62493b285" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019ddd5e-46ec-77d9-abf8-ddaa0c3c5910" xlink:to="loc_srt_ProductOrServiceAxis_019ddd5e-46ec-7209-8587-56d62493b285" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7209-8587-56d62493b285_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ddd5e-46ec-7209-8587-56d62493b285" xlink:to="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-7209-8587-56d62493b285_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-786e-ab0f-2ca4f064a7c7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ddd5e-46ec-7209-8587-56d62493b285" xlink:to="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-786e-ab0f-2ca4f064a7c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ZetoMember_019ddd5e-46ec-7b91-bb4d-20039f9c5e16" xlink:href="kzr-20260331.xsd#kzr_ZetoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-786e-ab0f-2ca4f064a7c7" xlink:to="loc_kzr_ZetoMember_019ddd5e-46ec-7b91-bb4d-20039f9c5e16" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_KZR261Member_019ddd5e-46ec-7649-a295-c3ab2f3c0464" xlink:href="kzr-20260331.xsd#kzr_KZR261Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ddd5e-46ec-786e-ab0f-2ca4f064a7c7" xlink:to="loc_kzr_KZR261Member_019ddd5e-46ec-7649-a295-c3ab2f3c0464" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_InternalCostsAbstract_019ddd5e-46ec-7d04-9a55-29dc31a9a38d" xlink:href="kzr-20260331.xsd#kzr_InternalCostsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_kzr_InternalCostsAbstract_019ddd5e-46ec-7d04-9a55-29dc31a9a38d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_019ddd5e-46ec-7099-9fd1-93f4c5a48e52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_InternalCostsAbstract_019ddd5e-46ec-7d04-9a55-29dc31a9a38d" xlink:to="loc_us-gaap_LaborAndRelatedExpense_019ddd5e-46ec-7099-9fd1-93f4c5a48e52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_ExternalCostsByProgramAbstract_019ddd5e-46ec-79e0-9e40-54b0bc768188" xlink:href="kzr-20260331.xsd#kzr_ExternalCostsByProgramAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_kzr_ExternalCostsByProgramAbstract_019ddd5e-46ec-79e0-9e40-54b0bc768188" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019ddd5e-46ec-7039-bdbc-4036d77a25fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_ExternalCostsByProgramAbstract_019ddd5e-46ec-79e0-9e40-54b0bc768188" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019ddd5e-46ec-7039-bdbc-4036d77a25fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019ddd5e-46ec-7abe-b066-148428396c10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_kzr_ExternalCostsByProgramAbstract_019ddd5e-46ec-79e0-9e40-54b0bc768188" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019ddd5e-46ec-7abe-b066-148428396c10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019ddd5e-46ec-7659-aae4-1814a4f976c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019ddd5e-46ec-7659-aae4-1814a4f976c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_019ddd5e-46ec-73e5-af25-5edbf3e47f12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_us-gaap_OperatingExpenses_019ddd5e-46ec-73e5-af25-5edbf3e47f12" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019ddd5e-46ec-7361-97cd-70a0de68fa05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_us-gaap_OperatingIncomeLoss_019ddd5e-46ec-7361-97cd-70a0de68fa05" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019ddd5e-46ec-798d-9609-5d7b6b1d69f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019ddd5e-46ec-798d-9609-5d7b6b1d69f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfOtherAssets_019de2c0-abc4-7746-a4be-68f1037a575b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_us-gaap_GainLossOnSaleOfOtherAssets_019de2c0-abc4-7746-a4be-68f1037a575b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_019ddd5e-46ec-7e7b-8d22-24dc048be875" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_us-gaap_InterestExpense_019ddd5e-46ec-7e7b-8d22-24dc048be875" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ddd5e-46ec-7e65-9bad-52ffb6d8c43e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019ddd5e-46ec-75be-b601-72676478e21c" xlink:to="loc_us-gaap_NetIncomeLoss_019ddd5e-46ec-7e65-9bad-52ffb6d8c43e" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.kezarlifesciences.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="kzr-20260331.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.kezarlifesciences.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019ddd5e-46ec-759f-b4e7-9d17ec528683" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019ddd5e-46ec-7849-964b-0e58de3609c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ddd5e-46ec-759f-b4e7-9d17ec528683" xlink:to="loc_us-gaap_SubsequentEventTable_019ddd5e-46ec-7849-964b-0e58de3609c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019ddd5e-46ec-72d8-8a2a-93ca8825a29b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ddd5e-46ec-7849-964b-0e58de3609c8" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019ddd5e-46ec-72d8-8a2a-93ca8825a29b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-46ec-72d8-8a2a-93ca8825a29b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019ddd5e-46ec-72d8-8a2a-93ca8825a29b" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-46ec-72d8-8a2a-93ca8825a29b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-46ec-7926-8fc9-95e8c62612f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019ddd5e-46ec-72d8-8a2a-93ca8825a29b" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-46ec-7926-8fc9-95e8c62612f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019ddd5e-46ec-74c4-9530-d140c4708e31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019ddd5e-46ec-7926-8fc9-95e8c62612f5" xlink:to="loc_us-gaap_SubsequentEventMember_019ddd5e-46ec-74c4-9530-d140c4708e31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019e028e-0291-75a8-939c-c7ab3f6a3f99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ddd5e-46ec-7849-964b-0e58de3609c8" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019e028e-0291-75a8-939c-c7ab3f6a3f99" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e028e-0291-75a8-939c-c7ab3f6a3f99_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e028e-0291-75a8-939c-c7ab3f6a3f99" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e028e-0291-75a8-939c-c7ab3f6a3f99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e028e-0291-7c55-9851-811aa3aa2273" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019e028e-0291-75a8-939c-c7ab3f6a3f99" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e028e-0291-7c55-9851-811aa3aa2273" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_KezarLifeSciencesIncMember_019e03df-21ee-7709-9e78-67f905439a13" xlink:href="kzr-20260331.xsd#kzr_KezarLifeSciencesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019e028e-0291-7c55-9851-811aa3aa2273" xlink:to="loc_kzr_KezarLifeSciencesIncMember_019e03df-21ee-7709-9e78-67f905439a13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e03da-e5cc-7bc5-ac8c-235cd566d58d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ddd5e-46ec-7849-964b-0e58de3609c8" xlink:to="loc_dei_LegalEntityAxis_019e03da-e5cc-7bc5-ac8c-235cd566d58d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e03da-e5cc-7bc5-ac8c-235cd566d58d_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e03da-e5cc-7bc5-ac8c-235cd566d58d" xlink:to="loc_dei_EntityDomain_019e03da-e5cc-7bc5-ac8c-235cd566d58d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e03da-e5cc-7829-9751-b6ab1135f9af" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e03da-e5cc-7bc5-ac8c-235cd566d58d" xlink:to="loc_dei_EntityDomain_019e03da-e5cc-7829-9751-b6ab1135f9af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_TangCapitalPartnersLPMember_019e03db-12f0-76e0-91f7-402831098f6f" xlink:href="kzr-20260331.xsd#kzr_TangCapitalPartnersLPMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e03da-e5cc-7829-9751-b6ab1135f9af" xlink:to="loc_kzr_TangCapitalPartnersLPMember_019e03db-12f0-76e0-91f7-402831098f6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019e03db-3b66-743a-b313-c732f10a6a38" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019ddd5e-46ec-7849-964b-0e58de3609c8" xlink:to="loc_srt_OwnershipAxis_019e03db-3b66-743a-b313-c732f10a6a38" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019e03db-3b66-743a-b313-c732f10a6a38_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019e03db-3b66-743a-b313-c732f10a6a38" xlink:to="loc_srt_OwnershipDomain_019e03db-3b66-743a-b313-c732f10a6a38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019e03db-3b66-799d-bc72-9a0c2c8344b2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019e03db-3b66-743a-b313-c732f10a6a38" xlink:to="loc_srt_OwnershipDomain_019e03db-3b66-799d-bc72-9a0c2c8344b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_KezarLifeSciencesIncMember_019e03db-5569-7195-b167-ce2cb4566084" xlink:href="kzr-20260331.xsd#kzr_KezarLifeSciencesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019e03db-3b66-799d-bc72-9a0c2c8344b2" xlink:to="loc_kzr_KezarLifeSciencesIncMember_019e03db-5569-7195-b167-ce2cb4566084" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_TerminationPayoutHealthInsurancePremiumWorth_019e03d5-0bd2-7263-b18f-4ce08c40dddb" xlink:href="kzr-20260331.xsd#kzr_TerminationPayoutHealthInsurancePremiumWorth"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ddd5e-46ec-759f-b4e7-9d17ec528683" xlink:to="loc_kzr_TerminationPayoutHealthInsurancePremiumWorth_019e03d5-0bd2-7263-b18f-4ce08c40dddb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019e03d6-93f7-77ba-b848-a294595d40ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ddd5e-46ec-759f-b4e7-9d17ec528683" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019e03d6-93f7-77ba-b848-a294595d40ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_019e03da-5bad-716e-acb2-3d616fc3905b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ddd5e-46ec-759f-b4e7-9d17ec528683" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_019e03da-5bad-716e-acb2-3d616fc3905b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionSharePrice_019e0287-dc17-70ea-aa1b-fc57d82cca0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionSharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ddd5e-46ec-759f-b4e7-9d17ec528683" xlink:to="loc_us-gaap_BusinessAcquisitionSharePrice_019e0287-dc17-70ea-aa1b-fc57d82cca0d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_kzr_BusinessCombinationNumberOfContingentValueRight_019e03e7-6897-73b6-89dc-5b43a2b5ea3f" xlink:href="kzr-20260331.xsd#kzr_BusinessCombinationNumberOfContingentValueRight"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019ddd5e-46ec-759f-b4e7-9d17ec528683" xlink:to="loc_kzr_BusinessCombinationNumberOfContingentValueRight_019e03e7-6897-73b6-89dc-5b43a2b5ea3f" xlink:type="arc" order="4"/>
  </link:definitionLink>
</link:linkbase>
