Prostaglandin E2 (PGE2), a major cyclooxygenase (COX) metabolite, plays important roles in tumor biology. We studied the role of EP2, a receptor for PGE2, in tumor angiogenesis using EP2 knockout mice. We found that deletion of the EP2 receptor impaired tumor angiogenesis and this finding was confirmed by an in vivo corneal angiogenesis model and an ex vivo aortic ring assay. To further characterize the cellular mechanisms of the EP2 receptor in angiogenesis, we isolated primary pulmonary endothelial cells (ECs) from wild-type (wt) and EP2-/- mice and observed that EP2-/- ECs exhibited defects in vascular branch formation when compared to wt ECs. In addition, EP2-/- ECs showed impaired cell motility on collagen-coated surface and they responded poorly to PGE2-induced cell migration compared to control cells. However, no difference in cell proliferation was observed between the EP2-/- and wt Ecs. In addition, EP2-/- ECs were more susceptible to apoptosis than wt cells under growth factor depletion conditions. Collectively, our data demonstrate that EP2 signaling in endothelium directly regulates tumor angiogenesis by contributing to cell survival and endothelial cell motility. Moreover, our finding suggests that EP2 is a major receptor in PGE2-mediated cell motility in ECs.