In enzymology, a lactaldehyde reductase (EC 1.1.1.77) is an enzyme that catalyzes the chemical reaction

(R)[or (S)]-propane-1,2-diol + NAD⁺ ${\displaystyle \rightleftharpoons }$ (R)[or (S)]-lactaldehyde + NADH + H⁺

The 3 substrates of this enzyme are (R)-propane-1,2-diol, (S)-propane-1,2-diol, and NAD⁺, whereas its 4 products are (R)-lactaldehyde, (S)-lactaldehyde, 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 (R)[or (S)]-propane-1,2-diol:NAD⁺ oxidoreductase. Other names in common use include propanediol:nicotinamide adenine dinucleotide (NAD⁺) oxidoreductase, and L-lactaldehyde:propanediol oxidoreductase. This enzyme participates in pyruvate metabolism and glyoxylate and dicarboxylate metabolism.

As of late 2007, 3 structures have been solved for this class of enzymes, with PDB accession codes 1RRM, 2BI4, and 2BL4.