Abstract: Objective：To study the specific mechanisms underlying the improvement of astragalus membranaceus（AM） on postmenopausal osteoporosis. Methods：A total of 40 three-month-old female SD rats were randomly divided into four groups: sham group, ovariectomized（ＯＶＸ） group, the AM group, and the antioxidant group. Four weeks after surgery, each group was respectively given their treatment by gavage. Animals were sacrificed at 12 weeks, and levels of oxidative stress in serum and bone tissue, femur bone density and bone metabolism were analyzed. Results：Significantly higher oxidative stress level and lower bone mineral density were observed in the OVX group than that in the sham group （all P＜0.01）. Compared with the OVX group, AM group and antioxidant group showed significantly reduced oxidative stress level （P＜0.01）, while the femur bone density was significantly increased （P＜0.05） and alkaline phosphatase and osteocalcin were significantly decreased （both P＜0.05）. Conclusions：AM extract can effectively improve bone loss and bone metabolism in ovariectomized rats, and this improvement was achieved by its antioxidant effect.

Key words: Astragalus membranaceus, Osteoporosis, Bone density, Animal experimentation