In enzymology, a nucleoside-triphosphatase (NTPase) () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are NTP and H<sub>2</sub>O, whereas its two products are NDP 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 unspecific diphosphate phosphohydrolase. Other names in common use include nucleoside triphosphate phosphohydrolase, nucleoside-5-triphosphate phosphohydrolase, and nucleoside 5-triphosphatase. This enzyme participates in purine metabolism and thiamine metabolism.
As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code .