In enzymology, a hydroxylamine reductase (NADH) () is an enzyme that catalyzes the chemical reaction.
The 3 substrates of this enzyme are NH<sub>3</sub>, NAD<sup>+</sup>, and H<sub>2</sub>O, whereas its 3 products are hydroxylamine, NADH, and H<sup>+</sup>.
This enzyme belongs to the family of oxidoreductases, specifically those acting on other nitrogenous compounds as donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is ammonium:NAD+ oxidoreductase. Other names in common use include hydroxylamine reductase, ammonium dehydrogenase, NADH-hydroxylamine reductase, N-hydroxy amine reductase, hydroxylamine reductase (NADH2), and NADH2:hydroxylamine oxidoreductase. This enzyme participates in nitrogen metabolism.