Objective To study the effects of soybean isoflavone(SI) on antioxidation and bone morphology in ovariectomized rats. Methods Seventy female SpragueDawley(SD) rats were randomly divided into 7 groups, according to the levels of total cholesterol in serum: highlipoids group, estrogen group, low dose SI group, middle dose SI group, high dose SI group, sham group and normal control group. A week after bilateral ovaries were excised except in the sham and normal control groups estrogen, different doses of SI or deionized water were fed with intragastric administration for 12 weeks. Body weights were measured every week and vena caudalis serum, innards tissue, femoral bone were collected immediately after the rats were ovariectomized or killed. The activity of alkaline phosphatase(AKP), superoxide dismutase(SOD), glutathione peroxidase(GSH-Px) in serum and bone density were measured respectively, with 63 SD rats being used for the experiment. Results In the intervention groups femoral bone weights were significantly higher than those in both the highlipoids and the control group. The activity of AKP、GSH-Px was increased after intervention, There was a same efficacy between high dose intervention and estrogen treatment on bone density. SI invention mitigated ovariectomyinduced bone loss.Conclusion The SI has some efficacy in ovariectomized rats antioxidation, activity of bone metabolism enzyme and can reverse bone loss. The decrease in bone density is interrupted under sufficient intervention. In view of phytoestrogen’s weak capability of binding with animals’ estrogen receptor(E