In enzymology, a (S)-carnitine 3-dehydrogenase (EC 1.1.1.254) is an enzyme that catalyzes the chemical reaction

(S)-carnitine + NAD⁺ ${\displaystyle \rightleftharpoons }$ 3-dehydrocarnitine + NADH + H⁺

Thus, the two substrates of this enzyme are (S)-carnitine and NAD⁺, whereas its 3 products are 3-dehydrocarnitine, 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 (S)-carnitine:NAD⁺ oxidoreductase.

• Setyahadi S, Ueyama T, Arimoto T, Mori N, Kitamoto Y (1997). "Purification and properties of a new enzyme, D-carnitine dehydrogenase, from Agrobacterium sp. 525a". Biosci. Biotechnol. Biochem. 61 (6): 1055–8. doi:10.1271/bbb.61.1055. PMID 9214773.