v3.25.2
Document and Entity Information - shares
 6 Months Ended
Jun. 30, 2025
Jul. 31, 2025
Document and Entity Information [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2025  
Document Transition Report false  
Entity File Number 001-42270  
Entity Registrant Name Zenas BioPharma, Inc.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 93-2749244  
Entity Address, Address Line One 852 Winter Street  
Entity Address, Adress Line Two Suite 250  
Entity Address, City or Town Waltham  
Entity Address State Or Province MA  
Entity Address, Postal Zip Code 02451  
City Area Code 857  
Local Phone Number 271-2954  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Shell Company false  
Title of 12(b) Security Common stock, par value $0.0001 per share  
Trading Symbol ZBIO  
Security Exchange Name NASDAQ  
Entity Common Stock, Shares Outstanding   42,110,313
Entity Central Index Key 0001953926  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q2  
Amendment Flag false