Document and Entity Information - USD ($)	12 Months Ended	48 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Mar. 31, 2022	Jun. 30, 2021
Document and Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-35853
Entity Registrant Name	BIOSTAGE, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-5210462
Entity Address, Address Line One	84 October Hill Road, Suite 11
Entity Address, City or Town	Holliston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01746
City Area Code	774
Local Phone Number	233-7300
Title of 12(b) Security	None
No Trading Symbol Flag	true
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding			10,760,871
Entity Central Index Key	0001563665
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
Title of 12(b) Security	None
Entity Public Float				$ 8,058,400
Auditor Name	Wei, Wei & Co., LLP	RSM US LLP
Auditor Firm ID	2388
Auditor Location	Flushing, New York	Boston, Massachusetts