In enzymology, a 12alpha-hydroxysteroid dehydrogenase (EC 1.1.1.176) is an enzyme that catalyzes the chemical reaction

3alpha,7alpha,12alpha-trihydroxy-5beta-cholanate + NADP⁺ ${\displaystyle \rightleftharpoons }$ 3alpha,7alpha-dihydroxy-12-oxo-5beta-cholanate + NADPH + H⁺

Thus, the two substrates of this enzyme are 3alpha,7alpha,12alpha-trihydroxy-5beta-cholanate and NADP⁺, whereas its 3 products are 3alpha,7alpha-dihydroxy-12-oxo-5beta-cholanate, NADPH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD⁺ or NADP⁺ as acceptor. The systematic name of this enzyme class is 12alpha-hydroxysteroid:NADP⁺ 12-oxidoreductase. Other names in common use include 12alpha-hydroxy steroid dehydrogenase, 12alpha-hydroxy steroid dehydrogenase, NAD⁺-dependent 12alpha-hydroxysteroid dehydrogenase, and NADP⁺-12alpha-hydroxysteroid dehydrogenase. This enzyme is involved in a metabolic pathway that degrades bile acids into cholesterol.