In enzymology, a glycolaldehyde dehydrogenase (EC 1.2.1.21) is an enzyme that catalyzes the chemical reaction

glycolaldehyde + NAD⁺ + H₂O ${\displaystyle \rightleftharpoons }$ glycolate + NADH + H⁺

The 3 substrates of this enzyme are glycolaldehyde, NAD⁺, and H₂O, whereas its 3 products are glycolate, NADH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is glycolaldehyde:NAD+ oxidoreductase. This enzyme is also called glycol aldehyde dehydrogenase. This enzyme participates in glyoxylate and dicarboxylate metabolism.

As of late 2007, 3 structures have been solved for this class of enzymes, with PDB accession codes 2HG2, 2ILU, and 2IMP.