This study was to investigated the effect of exogenous oxygen free radicals(OFR)on the rabbit basilar artery. Exogenous OFR were generated by electrolysis of Krebs' solution. The perfusion pressure and malonyldialdehyde content in basilar artery were increased, meanwhile release of endothelium derived relaxing factor,nitrite content and superoxide dismutase activity decreased after OFR damage, These data indicated that OFR induced cerebral vasospasm is mainly mediated by cerebral vascular endothelial damage and lipid peroxide formation.