Rac1, a subunit of NADPH oxidase, plays an important role in directed endothelial cell motility. We reported previously that Rac1 activation was necessary for choroidal endothelial cell migration across the retinal pigment epithelium, a critical step in the development of vision-threatening neovascular age-related macular degeneration. Here we explored the roles of Rac1 and NADPH oxidase activation in response to vascular endothelial growth factor treatment in vitro and in a model of laser-induced choroidal neovascularization. We found that vascular endothelial growth factor induced the activation of Rac1 and of NADPH oxidase in cultured human choroidal endothelial cells. Further, vascular endothelial growth factor led to heightened generation of reactive oxygen species from cultured human choroidal endothelial cells, which was prevented by the NADPH oxidase inhibitors, apocynin and diphenyleneiodonium, or the antioxidant, N-acetyl-L-cysteine. In a model of laser-induced injury, inhibition of NADPH oxidase with apocynin significantly reduced reactive oxygen species levels as measured by dihydroethidium fluorescence and the volume of laser-induced choroidal neovascularization. Mice lacking functional p47phox, a subunit of NADPH oxidase, had reduced dihydroethidium fluorescence and choroidal neovascularization compared with wild-type controls. Taken together, these results indicate that vascular endothelial growth factor activates Rac1 upstream from NADPH oxidase in human choroidal endothelial cells and increases generation of reactive oxygen species, contributing to choroidal neovascularization. These steps may contributed to the pathology of neovascular age-related macular degeneration.