In enzymology, a 4-phosphoerythronate dehydogenase (EC 1.1.1.290) is an enzyme that catalyzes the chemical reaction

4-phospho-D-erythronate + NAD⁺ ${\displaystyle \rightleftharpoons }$ (3R)-3-hydroxy-2-oxo-4-phosphonooxybutanoate + NADH + H⁺

Thus, the two substrates of this enzyme are 4-phospho-D-erythronate and NAD⁺, whereas its 3 products are (3R)-3-hydroxy-2-oxo-4-phosphonooxybutanoate, 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 4-phospho-D-erythronate:NAD⁺ 2-oxidoreductase. Other names in common use include PdxB, PdxB 4PE dehydrogenase, and 4-O-phosphoerythronate dehydrogenase. This enzyme participates in vitamin B₆ metabolism.

As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 2O4C.