In enzymology, L-galactonolactone oxidase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are L-galactono-1,4-lactone and oxygen. Its products are L-ascorbic acid and hydrogen peroxide.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donors with oxygen as acceptor. The systematic name of this enzyme class is L-galactono-1,4-lactone:oxygen 3-oxidoreductase. This enzyme is also called L-galactono-1,4-lactone oxidase. This enzyme participates in ascorbic acid and aldaric acid metabolism. It employs one cofactor, FAD.