Cover Document
| Cover Document | Aug. 16, 2019 |
| Cover page. | |
| Document Type | 8-K |
| Document Period End Date | Aug. 16, 2019 |
| Entity Registrant Name | MOLECULIN BIOTECH, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-37758 |
| Entity Tax Identification Number | 47-4671997 |
| Entity Address, Address Line One | 5300 Memorial Drive |
| Entity Address, Address Line Two | Suite 950 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Title of each class | Common Stock, par value $.001 per shares |
| Trading Symbol | MBRX |
| Name of each exchange on which registered | NASDAQ |
| Entity Central Index Key | 0001659617 |
| Amendment Flag | false |