In enzymology, a GDP-4-dehydro-6-deoxy-D-mannose reductase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are GDP-6-deoxy-D-mannose, NAD<sup>+</sup>, and NADP<sup>+</sup>, whereas its 4 products are GDP-4-dehydro-6-deoxy-D-mannose, NADH, NADPH, and H<sup>+</sup>.
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 GDP-6-deoxy-D-mannose:NAD(P)<sup>+</sup> 4-oxidoreductase (D-rhamnose-forming). Other names in common use include GDP-4-keto-6-deoxy-D-mannose reductase [ambiguous], GDP-6-deoxy-D-lyxo-4-hexulose reductase, and Rmd. This enzyme participates in fructose and mannose metabolism.