Abstract: Background Stromal cell-derived factor-1_α（SDF-1_α）has been demonstrated to be essential for stern cell mobilization/homing.Recent evidence indicates that SDF-1_α has been expressed in injured carotid arter- ies.Besides,high SDF-1_α plasma levels are clinically associated with stable coronary artery disease.Objective To investigate whether SDF 1 involves in mobilization of endothelial progenitor cells（EPC）and reendothelialization after vascular injury.Methods SDF-1_α was detected by RT-PCR and Western blot in carotid arteries of mice at different time points after wire-induced injury.SDF-1_α determination in peripheral blood samples and BM was per- formed by SDF-1_α enzyme-linked immunosorbent assay（ELISA）kit.EPC in peripheral blood collected at different time points after vascular injury were quantified by flow cytornetry.In subgroup,blocking SDF-1 rnonoclonal anti- body was injected,peripheral blood EPC were quantified after vascular injury and reendothelialization of injured ar- teries was determined 14 days later.Results Expression of SDF-1_α was evident at day 1,and peaked at day 3 after arterial injury.A rise in plasmatic concentration of SDF-1_α and a significant reduction of SDF-1_α in bone marrow concentration was noticed at all time points following injury.The amount of circulating EPC was increased shortly after induction of vascular injury and persisted up to 7 days（P＜0.01）.In SDF-1_α antibody-treated mice,only a little rise in the amount of circulating EPC was noted at day 1 after vascular injury and reduced reendothelialization area was observed 14 days later（P＜0.01）.Conclusion SDF-1_α plays an instrumental role in EPC mobilization and reendothelialization after vascular injury in mice.