Abstract: Objective To investig ate the effects of different dosag es of daidzein on histomorphometr y and bone biome chanics in ovariectomized rats.Methods 72 female SDrats of 3 months were divided into six groups by body weight r andomly.One group was sham group,and the o ther rats in 5 groups were operated to cut out their ov ar ies.Dr enched daidzein was given for 6 months and the r ats were killed.To measure geometr ic parameters,histomorphometry and bone biomechanics of the left femur in differ ent groups of rats were observed.Results The area percent of trabecular,the thickness and the number of tr abecular in OVX group were all reduced with percentage of 25.8%,8.09%,12.4%,respectively.The bone biology mechanics performance dropped,the maximum load and flexibility load dropped obviously.Some dosages of daidzein>50mg/(kg·bw)could antagonize these changes(P<0.05).Conclusion Some dosages of daidzein>50 mg/(kg·bw) can improve the histomor phometry and biomechanics of bone of gelding osteoporosis female rats.