In enzymology, a hydroxylamine reductase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are NH<sub>3</sub>, H<sub>2</sub>O, and acceptor, whereas its two products are hydroxylamine and reduced acceptor.
This enzyme belongs to the family of oxidoreductases, specifically those acting on other nitrogenous compounds as donors with other acceptors. The systematic name of this enzyme class is ammonia:acceptor oxidoreductase. Other names in common use include hydroxylamine (acceptor) reductase, and ammonia:(acceptor) oxidoreductase. This enzyme participates in nitrogen metabolism. It has 2 cofactors: FAD, and Flavoprotein.