o-Aminophenol oxidase (, isophenoxazine synthase, o-aminophenol:O<sub>2</sub> oxidoreductase, 2-aminophenol:O<sub>2</sub> oxidoreductase, GriF) is an enzyme with systematic name 2-aminophenol:oxygen oxidoreductase. This enzyme catalyses the following chemical reaction
o-Aminophenol oxidase is a flavoprotein. The product phenoxazine derivative can be incorporated into natural products like grixazone and actinomycin.