In enzymology, a thiol oxidase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are R'C(R)SH and O<sub>2</sub>, whereas its two products are R'C(R)S-S(R)CR' and H<sub>2</sub>O.
This enzyme belongs to the family of oxidoreductases, specifically those acting on a sulfur group of donors with oxygen as acceptor. The systematic name of this enzyme class is thiol:oxygen oxidoreductase. This enzyme is also called sulfhydryl oxidase.