In enzymology, a vanillate monooxygenase (EC 1.14.13.82) is an enzyme that catalyzes the chemical reaction

+ O₂ + NADH + H⁺ ${\displaystyle \rightleftharpoons }$ + NAD⁺ + H₂O + formaldehyde

The 4 substrates of this enzyme are vanillate, O₂, NADH, and H⁺, whereas its 4 products are 3,4-dihydroxybenzoate, NAD⁺, H₂O, and formaldehyde.

This enzyme belongs to the family of oxidoreductases, specifically those acting on paired donors, with O₂ as oxidant and incorporation or reduction of oxygen. The oxygen incorporated need not be derived from O₂ with NADH or NADPH as one donor, and incorporation of one atom o oxygen into the other donor. The systematic name of this enzyme class is vanillate:oxygen oxidoreductase (demethylating). Other names in common use include 4-hydroxy-3-methoxybenzoate demethylase, and vanillate demethylase. This enzyme participates in 2,4-dichlorobenzoate degradation.