The mechanisms of human bone marrow mesenchymal stem cells (hBMMSCs)-mediated immunomodulation are still not be completely clarified. In order to investigate the expression of B7-H1 on hBMMSCs and to explore whether B7-H1 mediated signaling pathway (B7-H1/PD-1) involves in the mechanisms of hBMMSCs-mediated immunomodulation, the hBMMSCs were isolated, cultured and identified, the B7-H1 expression on hBMMSCs was detected by flow cytometry, RT-PCR, and Western blot. The inhibitory effect of hBMMSCs on proliferation of T lymphocytes was observed in mixed lymphocyte culture, and then the functional anti-B7-H1 monoclonal antibody (mcAb) was used to block B7-H1, the proliferation of T lymphocytes was detected by using CCK-8. The results indicated that hBMMSCs highly expressed B7-H1 molecule, hBMMSCs effectively inhibited the proliferation of T lymphocytes with a dose-dependent manner, and the inhibitory proliferation of T lymphocytes by hBMMSCs could be partially restored when the anti-B7-H1 mAb was used to block the B7-H1, the inhibitory rate of T lymphocyte proliferation decreased from 64.1% to 38.75%. It is concluded that B7-H1 highly expresses on hBMMSCs, the B7-H1 mediated signaling pathway (B7-H1/PD-1) involves in the mechanisms for hBMMSCs-mediated immunomodulation.