3-ketosteroid 9alpha-monooxygenase (, KshAB, 3-ketosteroid 9alpha-hydroxylase) is an enzyme with systematic name androsta-1,4-diene-3,17-dione,NADH:oxygen oxidoreductase (9alpha-hydroxylating). This enzyme catalyses the following chemical reaction
3-Ketosteroid 9alpha-monooxygenase is involved in the cholesterol degradation in several bacterial pathogens.