In enzymology, galactitol-1-phosphate 5-dehydrogenase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are galactitol-1-phosphate and oxidised nicotinamide adenine dinucleotide (NAD<sup>+</sup>). Its 3 products are L-tagatose 6-phosphate (shown in its open-chain keto form), 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 galactitol-1-phosphate:NAD<sup>+</sup> oxidoreductase. This enzyme participates in galactose metabolism. It employs one cofactor, zinc.