Ketosteroid monooxygenase (, steroid-ketone monooxygenase, progesterone, NADPH2:oxygen oxidoreductase (20-hydroxylating, ester-producing), 17alpha-hydroxyprogesterone, NADPH<sub>2</sub>:oxygen oxidoreductase (20-hydroxylating, side-chain cleaving), androstenedione, NADPH<sub>2</sub>:oxygen oxidoreductase (17-hydroxylating, lactonizing)) is an enzyme with systematic name ketosteroid, NADPH:oxygen oxidoreductase (20-hydroxylating, ester-producing/20-hydroxylating, side-chain cleaving/17-hydroxylating, lactonizing). This enzyme catalyses the following chemical reaction
Ketosteroid monooxygenase is a single FAD-containing enzyme that catalyses three types of monooxygenase reaction.