In enzymology, a dimethylmalate dehydrogenase (EC 1.1.1.84) is an enzyme that catalyzes the chemical reaction

(R)-3,3-dimethylmalate + NAD⁺ ${\displaystyle \rightleftharpoons }$ 3-methyl-2-oxobutanoate + CO₂ + NADH

Thus, the two substrates of this enzyme are (R)-3,3-dimethylmalate and NAD⁺, whereas its 3 products are 3-methyl-2-oxobutanoate, CO₂, and NADH.

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 (R)-3,3-dimethylmalate:NAD⁺ oxidoreductase (decarboxylating). This enzyme is also called beta,beta-dimethylmalate dehydrogenase. This enzyme participates in pantothenate and coa biosynthesis. It has 5 cofactors: ammonia, manganese, cobalt, potassium, and NH₄⁺.