Endothelial dysfunction due to enhanced levels of reactive oxygen species (ROS) has been implicated in many cardiovascular disorders. The cyclic nucleotide phosphodiesterases (PDEs) control the levels of the second messengers cAMP and cGMP and have been implicated in the regulation of various vascular functions. Although PDE2 has the unique property to be activated by cGMP but to hydrolyze cAMP, its role in endothelial function is only poorly understood. Therefore we investigated whether PDE2 affects production of ROS, endothelial proliferation and angiogenesis in response to thrombin. Thrombin rapidly increased ROS production in human umbilical vein endothelial cells (HUVEC). Expression of siRNA specifically targeting PDE2 prevented thrombin-induced ROS production. Thrombin also rapidly stimulated the GTPase Rac1 which activates the ROS-generating NADPH oxidases. Depletion of PDE2 prevented this response. Similar results were observed upon application of an PDE2 inhibitor (PDP). Furthermore, thrombin-mediated endothelial proliferation and tube-forming ability were diminished upon depletion of PDE2. To confirm the involvement of PDE2 in new vessel formation in vivo, mouse aortic rings were cultured in collagen gels in the presence of lentiviral constructs expressing control siRNA or a siRNA targeting PDE2. Depletion of PDE2 prevented sprouting of new vessels. In addition we determined the role of PDE2 in a matrigel plug mouse angiogenesis model. Indeed, PDP injection to matrigel, reduced the angiogenetic response in vivo. These findings demonstrate that PDE2 promotes the activation of Rac1 and subsequent ROS production by thrombin resulting in endothelial proliferation and angiogenesis. Thus targeting PDE2 may provide a new therapeutic approach in diseases associated with endothelial dysfunction due to enhanced ROS production.