In enzymology, a 2,3-dihydroxybenzoate 3,4-dioxygenase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are 2,3-dihydroxybenzoate and O<sub>2</sub>, whereas its product is 3-carboxy-2-hydroxymuconate semialdehyde.
This enzyme belongs to the family of oxidoreductases, specifically those acting on single donors with O<sub>2</sub> as oxidant and incorporation of two atoms of oxygen into the substrate (oxygenases). The oxygen incorporated need not be derived from O<sub>2</sub>. The systematic name of this enzyme class is 2,3-dihydroxybenzoate:oxygen 3,4-oxidoreductase (decyclizing). Other names in common use include o-pyrocatechuate oxygenase, 2,3-dihydroxybenzoate 1,2-dioxygenase, 2,3-dihydroxybenzoic oxygenase, and 2,3-dihydroxybenzoate oxygenase. This enzyme participates in benzoate degradation via hydroxylation.