Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Nov. 01, 2020
Cover [Abstract]
Entity Registrant Name	Acer Therapeutics Inc.
Entity Central Index Key	0001069308
Document Type	10-Q
Document Period End Date	Sep. 30, 2020
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Trading Symbol	ACER
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		12,285,005
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2020
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-33004
Entity Tax Identification Number	32-0426967
Entity Address, Address Line One	One Gateway Center
Entity Address, Address Line Two	Suite 351
Entity Address, Address Line Three	300 Washington Street
Entity Address, City or Town	Newton
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02458
City Area Code	844
Local Phone Number	902-6100
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false