ObjectiveTo observe the effects of endovascular radiation (ER) on the proliferation and apoptosis of medial smooth muscle cells (SMC) and to discuss the possible mechanisms of radiation in the prevention of vascular restenosis (RS) in rabbits after carotid endarterectomy (CEA).MethodsForty rabbits undergoing CEA were randomly divided into four groups (each group=10) and given a radiation dose of 0, 10, 20 and 40 Gy 32P respectively. Rabbits were killed on the 3rd, 7th, 14th, 28th and 56th day after operation. The specimens were collected and histopathologic examinations were done.ResultsProliferation apparently occurred in the intima and media of carotid the lumen became narrow in the control group on the 14 th, 28 th and 56 th day after operation. While in the radiation groups, proliferation was apparently suppressed and the lumen was much less narrowed (P＜0.05). The apoptosis rate of SMCs and PCNA positive cells increased on the 3rd day after operation and reached the peak on the 7th day. There was statistical difference between the ER groups and control group (P＜0.01). The effects were much more evident in 20 Gy and 40 Gy groups compared with 10 Gy group (P＜0.01).ConclusionER may prevent RS by suppressing SMC proliferation and migration as well as inducing SMC apoptosis. The effects are positively correlated with radiation doses. SMC proliferation and apoptosis occur in the early period after balloon injury, while hyperplasia of intima and medial happens later.