3-hydroxyindolin-2-one monooxygenase (, BX4 (gene), CYP71C1 (gene)) is an enzyme with systematic name 3-hydroxyindolin-2-one,NAD(P)H:oxygen oxidoreductase (2-hydroxy-2H-1,4-benzoxazin-3(4H)-one-forming). This enzyme catalyses the following chemical reaction
3-hydroxyindolin-2-one monooxygenase is involved in the biosynthesis of protective and allelopathic benzoxazinoids in some plants.