In enzymology, a L-threonate 3-dehydrogenase (EC 1.1.1.129) is an enzyme that catalyzes the chemical reaction

L-threonate + NAD⁺ ${\displaystyle \rightleftharpoons }$ 3-dehydro-L-threonate + NADH + H⁺

Thus, the two substrates of this enzyme are L-threonate and NAD⁺, whereas its 3 products are 3-dehydro-L-threonate, 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 L-threonate:NAD⁺ 3-oxidoreductase. Other names in common use include threonate dehydrogenase, and L-threonic acid dehydrogenase. This enzyme participates in ascorbate and aldarate metabolism.