In enzymology, a GDP-mannose 6-dehydrogenase (EC 1.1.1.132) is an enzyme that catalyzes the chemical reaction

GDP-D-mannose + 2 NAD⁺ + H₂O ${\displaystyle \rightleftharpoons }$ GDP-D-mannuronate + 2 NADH + 2 H⁺

The 3 substrates of this enzyme are GDP-D-mannose, NAD⁺, and H₂O, whereas its 3 products are GDP-D-mannuronate, NADH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD⁺ or NADP⁺ as acceptor. The systematic name of this enzyme class is GDP-D-mannose:NAD⁺ 6-oxidoreductase. Other names in common use include guanosine diphosphomannose dehydrogenase, GDP-mannose dehydrogenase, guanosine diphosphomannose dehydrogenase, and guanosine diphospho-D-mannose dehydrogenase. This enzyme participates in fructose and mannose metabolism.

This protein may use the morpheein model of allosteric regulation.^[1]

As of late 2007, 3 structures have been solved for this class of enzymes, with PDB accession codes 1MFZ, 1MUU, and 1MV8.