v3.26.3
Cover - shares
 9 Months Ended
Sep. 30, 2026
Oct. 20, 2026
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 2026  
Document Transition Report false  
Entity File Number 001-40693  
Entity Registrant Name RALLYBIO CORPORATION  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 85-1083789  
Entity Address, Address Line One PO Box No. 325  
Entity Address, City or Town East Berlin  
Entity Address, State or Province CT  
Entity Address, Postal Zip Code 06023  
City Area Code 203  
Local Phone Number 859-3820  
Title of 12(b) Security Common Stock, par value $0.0001 per share  
Trading Symbol RLYB  
Security Exchange Name NASDAQ  
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  
Entity Bankruptcy Proceedings, Reporting Current true  
Entity Common Stock, Shares Outstanding (in shares)   5,383,937
Entity Central Index Key 0001739410  
Document Fiscal Year Focus 2026  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q3  
Amendment Flag false