In enzymology, an FMN reductase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are FMNH<sub>2</sub>, NAD<sup>+</sup>, and NADP<sup>+</sup>, whereas its 4 products are FMN, NADH, NADPH, and H<sup>+</sup>.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH group of donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is FMNH<sub>2</sub>:NAD(P)+ oxidoreductase. Other names in common use include NAD(P)H-FMN reductase, NAD(P)H-dependent FMN reductase, NAD(P)H:FMN oxidoreductase, NAD(P)H:flavin oxidoreductase, NAD(P)H<sub>2</sub> dehydrogenase (FMN), NAD(P)H<sub>2</sub>:FMN oxidoreductase, SsuE, riboflavin mononucleotide reductase, flavine mononucleotide reductase, riboflavin mononucleotide (reduced nicotinamide adenine dinucleotide, (phosphate)) reductase, flavin mononucleotide reductase, and riboflavine mononucleotide reductase.