In enzymology, a nitroquinoline-N-oxide reductase () is an enzyme that catalyzes the chemical reaction
The 4 substrates of this enzyme are 4-hydroxyaminoquinoline N-oxide, NAD<sup>+</sup>, NADP<sup>+</sup>, and H<sub>2</sub>O, whereas its 4 products are 4-nitroquinoline N-oxide, NADH, NADPH, 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 4-(hydroxyamino)quinoline N-oxide:NADP+ oxidoreductase. Other names in common use include 4-nitroquinoline 1-oxide reductase, 4NQO reductase, and NAD(P)H2:4-nitroquinoline-N-oxide oxidoreductase.