3-hydroxybenzoate 6-monooxygenase () is an enzyme that catalyzes the chemical reaction
The four substrates of this enzyme are 3-hydroxybenzoic acid, reduced nicotinamide adenine dinucleotide (NADH), oxygen and a proton. Its products are gentisic acid, oxidised NAD<sup>+</sup>, and water.
The enzyme is a flavin-containing monooxygenase that uses molecular oxygen as oxidant and incorporates one of its atoms into the starting material. The systematic name of this enzyme class is 3-hydroxybenzoate,NADH:oxygen oxidoreductase (6-hydroxylating). Other names in common use include 3-hydroxybenzoate 6-hydroxylase, m-hydroxybenzoate 6-hydroxylase, and 3-hydroxybenzoic acid-6-hydroxylase. It participates in benzoate degradation via hydroxylation and uses flavin adenine dinucleotide as a cofactor.