In enzymology, a rifamycin-B oxidase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are rifamycin B and O<sub>2</sub>, whereas its two products are rifamycin O and H<sub>2</sub>O<sub>2</sub>.
This enzyme belongs to the family of oxidoreductases, specifically those acting on diphenols and related substances as donor with oxygen as acceptor. The systematic name of this enzyme class is rifamycin-B:oxygen oxidoreductase. This enzyme is also called rifamycin B oxidase.