In enzymology, a NADPH:quinone reductase (EC 1.6.5.5) is an enzyme that catalyzes the chemical reaction

NADPH + H⁺ + 2quinone ${\displaystyle \rightleftharpoons }$ NADP⁺ + 2semiquinone

The 3 substrates of this enzyme are NADPH, H⁺, and quinone, whereas its two products are NADP⁺ and semiquinone.

This enzyme belongs to the family of oxidoreductases, specifically those acting on NADH or NADPH with a quinone or similar compound as acceptor. The systematic name of this enzyme class is NADPH:quinone oxidoreductase. This enzyme is also called NADPH2:quinone reductase.

As of late 2007, 3 structures have been solved for this class of enzymes, with PDB accession codes 1IYZ, 1IZ0, and 1YB5.