In enzymology, an ATP diphosphatase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are ATP and H<sub>2</sub>O, whereas its two products are AMP and diphosphate.
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 ATP diphosphohydrolase (diphosphate-forming). Other names in common use include ATPase, ATP pyrophosphatase, adenosine triphosphate pyrophosphatase, and ATP diphosphohydrolase [ambiguous]. This enzyme participates in purine metabolism and pyrimidine metabolism.