In enzymology, a triphosphatase (EC 3.6.1.25) is an enzyme that catalyzes the chemical reaction

triphosphate + H₂O ${\displaystyle \rightleftharpoons }$ diphosphate + phosphate

Thus, the two substrates of this enzyme are triphosphate and H₂O, whereas its two products are diphosphate and phosphate.

This enzyme belongs to the family of hydrolases, specifically those acting on acid anhydrides in phosphorus-containing anhydrides. The systematic name of this enzyme class is triphosphate phosphohydrolase. This enzyme is also called inorganic triphosphatase.