In enzymology, a dihydropyrimidinase (EC 3.5.2.2) is an enzyme that catalyzes the chemical reaction Thus, the two substrates of this enzyme are 5,6-dihydrouracil and H2O, whereas its product is 3-ureidopropanoate.

This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in cyclic amides.

The systematic name of this enzyme class is 5,6-dihydropyrimidine amidohydrolase.

Other names in common use include hydantoinase, hydropyrimidine hydrase, hydantoin peptidase, pyrimidine hydrase, and D-hydantoinase.

As of late 2007, 10 structures have been solved for this class of enzymes, with PDB accession codes 1GKP, 1GKQ, 1GKR, 1NFG, 1YNY, 2FTW, 2FTY, 2FVK, 2FVM, and 2GSE.