Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 04, 2021
Document Information [Line Items]
Entity Central Index Key	0001659617
Entity Registrant Name	Moleculin Biotech, Inc.
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2021
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-37758
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-4671997
Entity Address, Address Line One	5300 Memorial Drive
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77007
City Area Code	713
Local Phone Number	300-5160
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Small Business	true
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	MBRX
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		28,444,425