In enzymology, a 2,5-dioxopiperazine hydrolase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are 2,5-dioxopiperazine and H<sub>2</sub>O, whereas its product is glycylglycine.
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 2,5-dioxopiperazine amidohydrolase. Other names in common use include cyclo(Gly-Gly) hydrolase, and cyclo(glycylglycine) hydrolase.