In enzymology, a phosphonate dehydrogenase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are phosphonate, NAD<sup>+</sup>, and H<sub>2</sub>O, whereas its 3 products are phosphate, NADH, and H<sup>+</sup>.
This enzyme belongs to the family of oxidoreductases, specifically those acting on phosphorus or arsenic in donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is phosphonate:NAD+ oxidoreductase. Other names in common use include NAD:phosphite oxidoreductase, and phosphite dehydrogenase.