['To investigate the molecular pathway of substance P (SP) to induce osteoblastic differentiation.', 'Mesenchymal stem cells were isolated and cultured. The cultures were divided into four groups with Group A (control group) cultured without any factors, Group B cultured with SP, Group C cultured with SP and SP receptor neurokinin-1 (NK1) antagonist, and Group D cultured with SP NK1 antagonist respectively to induce osteoblastic cells differentiation. Osterix gene expression was detected by reverse transcription-polymerase chain reaction (RT-PCR) for three times after 1-2 weeks of cultivation and the results were analyzed by one-way analysis of variance (ANOVA).', 'The log phase of bone marrow stromal cells appeared at 4-6 days. ALP staining revealed that the majority of cells, more than 95%, were positive and small blue-purple granules were found in the cytoplasm. And Group B, treated with SP, showed a higher level of ALP activity than the other three groups. Meanwhile, RT-PCR found that Osterix expression in Group B was obviously up-regulated, compared with other groups. But Osterix expression in Group D had no remarkable differences, compared with the controls.'] Does substance P stimulate differentiation of mice osteoblast through up-regulating Osterix expression?