In enzymology, a methylarsonate reductase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are methylarsonate and glutathione, whereas its 3 products are methylarsonite, glutathione disulfide, and H<sub>2</sub>O.
This enzyme belongs to the family of oxidoreductases, specifically those acting on phosphorus or arsenic in donor with disulfide as acceptor. The systematic name of this enzyme class is gluthathione:methylarsonate oxidoreductase. This enzyme is also called MMA(V) reductase.