In enzymology, 4-hydroxymandelate oxidase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are (S)-4-Hydroxymandelic acid and oxygen. Its products are 4-hydroxybenzaldehyde, carbon dioxide, and hydrogen peroxide.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with oxygen as acceptor. The systematic name of this enzyme class is (S)-2-hydroxy-2-(4-hydroxyphenyl)acetate:oxygen 1-oxidoreductase. This enzyme is also called L-4-hydroxymandelate oxidase (decarboxylating). It has 2 cofactors: FAD, and Manganese.