Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 01, 2019
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Amendment Flag false  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Trading Symbol UBX  
Entity Registrant Name Unity Biotechnology, Inc.  
Entity Central Index Key 0001463361  
Current Fiscal Year End Date --12-31  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Current Reporting Status Yes  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Common Stock, Shares Outstanding   45,941,750
Entity Shell Company false  
Entity File Number 001-38470  
Entity Tax Identification Number 26-4726035  
Entity Incorporation, State or Country Code DE  
Entity Address, Address Line One 3280 Bayshore Blvd  
Entity Address, Address Line Two Suite 100  
Entity Address, City or Town Brisbane  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 94005  
City Area Code 650  
Local Phone Number 416-1192  
Title of 12(b) Security Common Stock, par value $0.0001  
Security Exchange Name NASDAQ