Aim To investigate the effect of estradiol on inhibition of neointimal proliferation after rat carotid artery balloon injury. Methods Eight-ten week-old S-D rats were divided into intact control group (n=7), gonadectomized control group (n=7) and estradiol (n=7,gonadectomization)group in each sex. Left carotid artery was not injured with 2.0F PTCA balloon until estradiol had been injected for three days. Rats were killed after injury two weeks later. Neointimal areas, ratios of intimal areas and media areas were measured with computer. Results Neointimal areas and ratios of inttimal areas and media areas in male in estradiol group were significantly less than those in intact control group (allP<0.01), and in gonadectomized control group (allP<0.05). Those in female ,in estradiol group were less than those in godectomized control group evidently (allP<0.01),were also similar to those in intact control group (all P>0.05). Conclusion Estradiol inhibited neointimal proliferation after the gonadectomized rat carotid artery balloon injury.