In enzymology, a methylguanidinase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are methylguanidine and H<sub>2</sub>O, whereas its two products are methylamine and urea.
This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in linear amidines. The systematic name of this enzyme class is methylguanidine amidinohydrolase. This enzyme is also called methylguanidine hydrolase.