Objective:To investigate the effect of bone marrow derived mesenchymal stem cells (BMSC) transplantation on bone metabolism and its mechanism in ovariectomized osteoporosis rats.Methods:Forty clean SD female rats aged 7 weeks were divided into 4 groups according to the random number table method: sham operation group, model group, the transplantation group, positive control group, in addition to control the rest of the group were performed bilateral oophorectomy build osteoporosis rats model, after 2 months of model establishment, rats in transplantation group were injected with 80 μl/kg PBS solution containing bone marrow mesenchymal stem cells through tail vein, rats in sham operation group and model group were injected with the same amount of PBS solution through tail vein, and rats in positive control group were given Xianlinggubao (0.5 g/100 g) by gavage every day. Serum and femur were collected 14 days after treatment. Hematoxylin and eosin staining (HE) was used to observe the histopathological changes of femur. Micro-CT was used to measure bone mineral density and bone parameters. The expression levels of osteocalcin, osteoprotegerin, alkaline phosphatase and insulin-like growth factor 1 were detected by enzyme-linked immunosorbent assay (ELISA) kit. The serum levels of calcium, phosphorus and magnesium were measured by spectrophotometer. The protein expressions of RANKL, OPG, TRAF6 and NF-KB1 in femur of each group were detected by Western blot.Results:Compared with the sham operation group, the bone mineral density (BMD) of the model group was decreased by (0.28±0.01) g/cm 3, bone volume fraction (BMD) was decreased by (0.28±0.01) g/cm 3. BV/TV) decreased by (19.73±2.02) %, trabecular thickness (Tb.Th) decreased by (0.082±0.008) mm, trabecular number (Tb.N) decreased by (1.60±0.17) mm -1 and trabecular separation/spacing (Tb.Sp) increased (0.273±0.024) mm, osteoprotegerin (489.49±55.29) ng/L, alkaline phosphatase (229.13±15.05) U/L, insulin-like growth factor-1 (236.64±14.32) μg/L, and osteocalcin were decreased (1.866±0.109) μg/L, calcium (11.98±1.09) mg/dl, phosphorus (6.85±0.68) mg/dl, and magnesium decreased (0.62±0.04) mg/dl) , the relative expression level of RANKL increased (1.05±0.09) , the relative expression level of OPG decreased (0.58±0.08) , the relative expression level of RANKL increased (0.74±0.10) , and the relative expression level of NF-kB1 increased (1.01±0.11) ( P<0.05) ; bone mineral density, bone mineral density, bone mineral density BMD (0.38±0.04 g/cm 3, BV/TV (26.73±2.74) %, Tb.Th (0.094±0.006) mm, Tb.N (2.67±0.09) mm-1 and Tb.Sp were decreased (0.241±0.026) mm) , osteoprotegerin (720.09±67.41) ng/L, alkaline phosphatase (269.48±14.15) U/L, insulin-like growth factor 1 (IGF-1) decreased (335.95±24.13) μg/L, and osteocalcin increased (1.392±0.153) μg/L, calcium (7.12±0.53) mg/dl, phosphorus (4.54±0.32) mg/dl, magnesium (0.87±0.08) mg/dl. RANKL relative expression level increased (0.59±0.05) , OPG relative expression level decreased (0.97±0.10) , RANKL relative expression level increased (0.45±0.06) , NF-kB1 relative expression level increased (0.72±0.06) ( P<0.05) ;bone mineral density, bone mineral density, bone mineral density BMD (0.36±0.05) g/cm 3, BV/TV (28.72±3.20) %, Tb.Th (0.096±0.011) mm, Tb.N (2.85±0.24) mm -1 Tb.Sp was basically unchanged (0.241±0.027) mm, osteoprotegerin was decreased (716.78±36.90) ng/L, alkaline phosphatase was basically unchanged (270.65±18.59) U/L, and insulin-like growth factor 1 was decreased (336.94±17.50) μg/L, osteocalcin (1.377±0.101) μg/L, calcium (7.13±0.80) mg/dl, phosphorus (4.58±0.71) mg/dl, and magnesium (0.89±0.04) remained unchanged mg/dl, the relative expression level of RANKL increased (0.55±0.08) , the relative expression level of OPG decreased (0.98±0.13) , the relative expression level of RANKL was basically unchanged (0.40±0.05) , and the relative expression level of NF-kB1 increased (0.65±0.09) ( P<0.05) . Conclusion:Bone marrow mesenchymal stem cell transplantation can improve osteoporosis in ovariectomized rats by regulating bone metabolism and serum levels of calcium, phosphorus and magnesium, which may be related to RANKL/OPG/TRAF6 pathway.