Somatic mutations in NRAS drive the pathogenesis of melanoma and other cancers but their role in vascular anomalies and specifically human endothelial cells is unclear. The goals of this study were to determine whether the somatic-activating NRAS^Q61R mutation in human endothelial cells induces abnormal angiogenesis and to develop in vitro and in vivo models to identify disease-causing pathways and test inhibitors. Here, we used mutant NRAS^Q61R and wild-type NRAS (NRAS^WT) expressing human endothelial cells in in vitro and in vivo angiogenesis models. These studies demonstrated that expression of NRAS^Q61R in human endothelial cells caused a shift to an abnormal spindle-shaped morphology, increased proliferation, and migration. NRAS^Q61R endothelial cells had increased phosphorylation of ERK compared to NRAS^WT cells indicating hyperactivation of MAPK/ERK pathways. NRAS^Q61R mutant endothelial cells generated abnormal enlarged vascular channels in a 3D fibrin gel model and in vivo, in xenografts in nude mice. These studies demonstrate that NRAS^Q61R can drive abnormal angiogenesis in human endothelial cells. Treatment with MAP kinase inhibitor U0126 prevented the change to a spindle-shaped morphology in NRAS^Q61R endothelial cells, whereas mTOR inhibitor rapamycin did not.