Cover - shares	3 Months Ended
	Mar. 31, 2020	May 06, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-37758
Entity Registrant Name	MOLECULIN BIOTECH, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-4671997
Entity Address, Street Address	5300 Memorial Drive,
Entity Address, Suite	Suite 950
Entity Address, City	Houston
Entity Address, State	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 Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Title of each class	Common Stock, par value $0.001 per share
Trading Symbol	MBRX
Name of each exchange on which registered	NASDAQ
Entity Common Stock, Shares Outstanding		60,403,164
Entity Central Index Key	0001659617
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Current Fiscal Year End Date	--12-31