Objective To explore the bone mineral density, micro-structure and biomechanical changes of the lumbar on rats induced by ovary irradiation. Methods The ovaries of rats were irradiated by 50Gy γ-ray to establish the animal model.The lumbar was got after 90 days. Dual energy X-ray absorpt metry (DEXA ) was used to measure the bone mineral density (BMD). The changes of bone microstructure characters were observed by the scanning electron microscope. Bone biomechanical properties were determined by the maximal loading obtained from the compression test. Results compared with the sham operated group, BMD of the ovary irradiated group was obviously lower(P<0.05), bone microstructure was destructive, and bone biomechanical properties were decreased(P<0.05). Conclusion Osteoporosis of the lumbar was induced by the ovary irradiation on rats.