In enzymology, a phosphoinositide 5-phosphatase (EC 3.1.3.36) is an enzyme that catalyzes the chemical reaction

1-phosphatidyl-1D-myo-inositol 4,5-bisphosphate + H2O {\displaystyle \rightleftharpoons } \rightleftharpoons 1-phosphatidyl-1D-myo-inositol 4-phosphate + phosphate Thus, the two substrates of this enzyme are 1-phosphatidyl-1D-myo-inositol 4,5-bisphosphate and H2O, whereas its two products are 1-phosphatidyl-1D-myo-inositol 4-phosphate and phosphate.

This enzyme belongs to the family of hydrolases, specifically those acting on phosphoric monoester bonds. The systematic name of this enzyme class is phosphatidyl-myo-inositol-4,5-bisphosphate 4-phosphohydrolase. Other names in common use include type II inositol polyphosphate 5-phosphatase, triphosphoinositide phosphatase, IP3 phosphatase, PtdIns(4,5)P2 phosphatase, triphosphoinositide phosphomonoesterase, diphosphoinositide phosphatase, inositol 1,4,5-triphosphate 5-phosphomonoesterase, inositol triphosphate 5-phosphomonoesterase, phosphatidylinositol-bisphosphatase, phosphatidyl-myo-inositol-4,5-bisphosphate phosphatase, phosphatidylinositol 4,5-bisphosphate phosphatase, polyphosphoinositol lipid 5-phosphatase, and phosphatidyl-inositol-bisphosphate phosphatase. This enzyme participates in inositol phosphate metabolism and phosphatidylinositol signaling system.