In enzymology, a 2,3-dihydroxybenzoate 3,4-dioxygenase (EC 1.13.11.14) is an enzyme that catalyzes the chemical reaction

2,3-dihydroxybenzoate + O₂ ${\displaystyle \rightleftharpoons }$ 3-carboxy-2-hydroxymuconate semialdehyde

Thus, the two substrates of this enzyme are 2,3-dihydroxybenzoate and O₂, whereas its product is 3-carboxy-2-hydroxymuconate semialdehyde.

This enzyme belongs to the family of oxidoreductases, specifically those acting on single donors with O₂ as oxidant and incorporation of two atoms of oxygen into the substrate (oxygenases). The oxygen incorporated need not be derived from O₂. 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.