In enzymology, a mannitol-1-phosphate 5-dehydrogenase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are D-mannitol 1-phosphate and oxidised nicotinamide adenine dinucleotide (NAD<sup>+</sup>). Its products are fructose 6-phosphate, reduced NADH and a proton.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD<sup>+</sup> or NADP<sup>+</sup> as acceptor. The systematic name of this enzyme class is D-mannitol-1-phosphate:NAD<sup>+</sup> 2-oxidoreductase. Other names in common use include hexose reductase, mannitol 1-phosphate dehydrogenase, D-mannitol-1-phosphate dehydrogenase, and fructose 6-phosphate reductase. This enzyme participates in fructose and mannose metabolism.