Objective To evaluate the bone repair capacity ofpolylactic acid-polyglycolic acid copolymer (PLGA)/collagen type Ⅰ (CoI) microspheres combined with BMSCs after being injected in intertrochanteric bone defect of osteoporotic female rats.Methods Prepared PLGA microspheres.The microspheres were coated with Col.BMSCs of the third passage were cultured with PLGA/CoI microspheres.Forty 3-month-old female SD rats were ovariectomized to establish osteoporotic animal models.The osteoporotic rats were randomly divided into 5 groups,including SHAM group,PBS group,Cell group,MS group and Cell+ MS group.There were 8 rats in each group.Different material was injected into the intertrochanteric bone defect site which was made with electric drill.Four rats of each group were sacrificed at 1 month and 3 months post-operation.The fenora were taken to measure the intertrochanteric bone mineral density (BMD) with DEXA and evaluate trabecular stucture with Micro CT.Results After 7 days of coculture,BMSCs seeded on PLGA/CoI microspheres had nice adherance and proliferation.There was no difference of BMC and BMD among all groups at 1 month post-operation.Tb.Th of Cell+MS group was higher than that of PBS group and MS group at 1 month post-operation.％Tb.Ar of Cell+MS group was higher than that of Cell group and MS group at 1 month post-operation.Tb.Sp of Cell+MS group had a tendence to decrease compared with other groups but there was no statistical difference at 1 month post-operation.After 3 months of operation,the BMC of Cell+MS group had a tendence to increase compared with that of PBS group and MS group but showed no statistical difference.BMD and Tb.Th of Cell+MS group was higher than those of other groups.％Tb.Ar of Cell+MS group was higher than that of SHAM group and PBS group.Tb.Sp of Cell+MS group had a tendence to reduce compared with other groups but showed no statistical difference.Conclusion The bone defect of osteoporotic site can be repaired 1 month after the injection of the PLGA/CoI microspheres combined with BMSCs.The trabecular reconstruction and bone quality of osteoporotic site can be improved 3 months after the injection.