In enzymology, an oxalate oxidase (EC 1.2.3.4) is an oxalate degrading enzyme that catalyzes the chemical reaction:

oxalate + O₂ + 2 H⁺ ${\displaystyle \rightleftharpoons }$ 2 CO₂ + H₂O₂

The 3 substrates of this enzyme are oxalate, O₂, and H⁺, whereas its two products are CO₂ and H₂O₂.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with oxygen as acceptor. The systematic name of this enzyme class is oxalate:oxygen oxidoreductase. Other names in common use include aero-oxalo dehydrogenase, and oxalic acid oxidase. This enzyme participates in glyoxylate and dicarboxylate metabolism. It uses Manganese as a cofactor.

As of late 2007, 4 structures have been solved for this class of enzymes, with PDB accession codes 1FI2, 2ET1, 2ET7, and 2ETE.