In enzymology, a cucurbitacin Delta23-reductase (EC 1.3.1.5) is an enzyme that catalyzes the chemical reaction

23,24-dihydrocucurbitacin + NAD(P)+ ${\displaystyle \rightleftharpoons }$ cucurbitacin + NAD(P)H + H⁺

The 3 substrates of this enzyme are 23,24-dihydrocucurbitacin, NAD⁺, and NADP⁺, whereas its 4 products are cucurbitacin, NADH, NADPH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is 23,24-dihydrocucurbitacin:NAD(P)+ Delta23-oxidoreductase. This enzyme is also called NAD(P)H: cucurbitacin B Delta23-oxidoreductase. It employs one cofactor, manganese.

• Schabort JC, Potgieter DJ (1968). "Cucurbitacin B delta 23-reductase from Cucurbita maxima. II Cofactor requirements, enzyme kinetics, substrate specificity and other characteristics". Biochim. Biophys. Acta. 151 (1): 47–53. doi:10.1016/0005-2744(68)90159-9. PMID 4384331.
• Schabort JC, Potgieter DJ, de Villiers V (1968). "Cucurbitacin B delta 23-reductase from Cucurbita maxima. I. Assay methods, isolation and purification". Biochim. Biophys. Acta. 151 (1): 33–46. doi:10.1016/0005-2744(68)90158-7. PMID 5640163.