Abstract: Objective To provide the theoretical evidence for the development of Traditional Chinese Medicine in treatment of osteoporosis by studying the effect of icariin（ICA） on osteoporosis in ovariectomized female rats. Methods Sixty healthy female Wistar rats at the age of 3 months were randomly divided into control group（sham group）,ovariectomized group（OVX group） and ICA group（20 in each group）.After a model was established,rats in ICA group received 10ml/kg intragastric ICA at the concentration of 30mg/ml,once a day for 90 days.All rats were killed and blood was taken from their femoral arteries to measure their blood serum estradiol,alkaline phosphatase（ALP） and tartrate-resistant acid phosphatase 5b（TRAP5b） levels and detect their lumbar vertebrae,femur and whole body bone densities by dual energy X-ray absorptiometry（DEXA）.After all rats were killed by cervical breaking,both femora were collected.The left femur tissue was cut into sections for histopathological study and total RNA was isolated from the right femur with a homogenizer.Expression levels of OPG,BMP-2 and COL-Ⅰ mRNA were measured by RT-PCR. Results The mean estradiol level was significantly lower while the alkaline phosphatase level was significantly higher in OVX group and ICA Group than in sham group（P＜0.01）.The TRAP5b level was significantly higher in OVX group than in sham group and ICA group（P＜0.01）.The lumbar vertebrae density and whole body bone density were higher in sham group and ICA group than in OVX group（P＜0.05） while the femoral bone density was higher in sham group than in OVX group（P＜0.05）.However,no significant difference was found in femoral bone density between ICA group and OVX group.The expression levels of OPG,BMP-2 and COL-ⅠmRNA were significantly higher in sham group and ICA group than in OVX group（P＜0.01）.No thinned and broken bone trabeculae and cortical bones were found in sham group and ICA group.However,severe osteoporosis occurred in OVX group. Conclusion ICA plays a role in prevention and treatment of osteoporosis in castrated female rats.