Objective:To investigate the therapeutic effect and mechanism of ovary tissue allotransplantation on the osteoporosis of ovariectomized rat model. Methods: 40 female SD rats were randomly divided into four groups: sham operation group, ovariectomized model group, estrogen replacement group and ovary allotransplantation group. The ovariectomized model was built by removing bilateral ovaries from backside. After ovariectomization, allogeneic ovary tissue was implanted to muscular layer of back to build ovary allotransplantation model. The rats of estrogen replacement group were intragastric administrated with 0.06 mg/kg estrogen for three months, while rats of other groups were intragastric administrated with same volume of normal saline (NS). After treatment, the body weight and the wet weight of uterus were weighed to calculate the uterus weight index. Morphology of vaginal epithelial and bone cells stained by HE was observed under light microscope. Moreover, bone mineral density (BMD) of whole body, proximal femur and proximal tibia were measured by dual energy xray absorptiometry (DXA). Serum estradiol (E2) was measured by radioimmunoassay. Results: Compared with sham operation group, the uterus weight index of the model group significantly declined（P<0.01）. The content of serum estradiol  significantly reduced（P<0.01）. Vaginal epithelial cells were small and not keratinized. The number of bone trabecula in the femur  markedly decreased. Bone absorption was obvious, which was shown as “islands”. Few marrow stromal cells existed in the expanded cavity of bone. Bone mineral density of whole body, femur and tibia of ovariectomized model group  reduced significantly（P all <0.01）. However, compared with ovariectomized model group, the uterus weight indexes and serum estradiol of the estrogen replacement and ovary allotransplantation group  significantly increased（P all<0.01）. Pathological sections showed that vaginal epithelial cells of both groups were keratinized mostly.  In the estrogen replacement group, cortical bone  thickened. Bone trabecula was strong with regular arrangement, large number and small space. The number of marrow stromal cells  increased in the reduced cavity of bone. In the ovary allotransplantation group, the area of cortical bone was expanded. Besides increased numbers, the area of bone trabecula was also enlarged and the space  reduced obviously. The connections  increased and ordered. Marrow stromal cells were well distributed. Conclusions: Transplanted ovary tissue may connect with muscular tissue via angiogenesis and then secrete endogenous estrogen. Estrogen can bind receptors of uterus, vagina and femur to maintain morphology and function of these target organs and inhibit the loss of bone mineral, leading to improvement of endocrine function of rats.