In enzymology, an endopolyphosphatase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are polyphosphate and H<sub>2</sub>O, whereas its product is oligophosphate.
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 polyphosphate polyphosphohydrolase. Other names in common use include polyphosphate depolymerase, metaphosphatase, polyphosphatase, and polymetaphosphatase.