In enzymology, a 3-oxo-5beta-steroid 4-dehydrogenase (EC 1.3.99.6) is an enzyme that catalyzes the chemical reaction

a 3-oxo-5beta-steroid + acceptor ${\displaystyle \rightleftharpoons }$ a 3-oxo-Delta₄-steroid + reduced acceptor

Thus, the two substrates of this enzyme are 3-oxo-5beta-steroid and acceptor, whereas its two products are 3-oxo-Delta4-steroid and reduced acceptor.

This enzyme belongs to the family of oxidoreductases, to be specific, those acting on the CH-CH group of donor with other acceptors. The systematic name of this enzyme class is 3-oxo-5beta-steroid:acceptor Delta4-oxidoreductase. This enzyme is also called 3-oxo-5beta-steroid:(acceptor) Delta4-oxidoreductase. This enzyme participates in 3 metabolic pathways: bile acid biosynthesis, c21-steroid hormone metabolism, and androgen and estrogen metabolism.

• Davidson SJ, Talalay P (1966). "Purification and mechanism of action of a steroid delta-4-5-beta-dehydrogenase". J. Biol. Chem. 241 (4): 906–15. PMID 5907467.