In enzymology, a citrullinase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are L-citrulline and H<sub>2</sub>O, whereas its 3 products are L-ornithine, CO<sub>2</sub>, and NH<sub>3</sub>.
This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in linear amides. The systematic name of this enzyme class is L-citrulline N5-carbamoyldihydrolase. Other names in common use include citrulline ureidase, citrulline hydrolase, and L-citrulline 5-N-carbamoyldihydrolase.