Inositol 1, 4, 5-trisphosphate receptor–mediated (IP 3 R-mediated) calcium (Ca 2+) release has been proposed to play an important role in regulating vascular smooth muscle cell (VSMC) contraction for decades. However, whether and how IP 3 R regulates blood pressure in vivo remains unclear. To address these questions, we have generated a smooth muscle–specific IP 3 R triple-knockout (smTKO) mouse model using a tamoxifen-inducible system. In this study, the role of IP 3 R-mediated Ca 2+ release in adult VSMCs on aortic vascular contractility and blood pressure was assessed following tamoxifen induction. We demonstrated that deletion of IP 3 Rs significantly reduced aortic contractile responses to vasoconstrictors, including phenylephrine, U46619, serotonin, and endothelin 1. Deletion of IP 3 Rs also dramatically reduced the phosphorylation of MLC20 and MYPT1 induced by U46619. Furthermore, although the basal blood pressure of smTKO mice remained similar to that of wild-type controls, the increase in systolic blood pressure upon chronic infusion of angiotensin II was significantly attenuated in smTKO mice. Taken together, our results demonstrate an important role for IP 3 R-mediated Ca 2+ release in VSMCs in regulating vascular contractility and hypertension.