In enzymology, a carboxymethylhydantoinase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are L-5-carboxymethylhydantoin and H<sub>2</sub>O, whereas its product is N-carbamoyl-L-aspartate.
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 L-5-carboxymethylhydantoin amidohydrolase. This enzyme is also called hydantoin hydrolase.