In enzymology, phthalate 4,5-cis-dihydrodiol dehydrogenase () is an enzyme that catalyzes the chemical reaction
The two substrates of this enzyme are cis-4,5-dihydroxycyclohexa-2,6-diene-1,2-dicarboxylic acid and oxidised nicotinamide adenine dinucleotide (NAD<sup>+</sup>). Its products are 4,5-dihydroxyphthalic acid, reduced NADH, and a proton.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is cis-4,5-dihydroxycyclohexa-1(6),2-diene-1,2-dicarboxylate:NAD+ oxidoreductase. This enzyme participates in 2,4-dichlorobenzoate degradation.