Objective:To investigate the protective effect and mechanism of bone marrow-derived mesenchymal stem cell (BM-MSC) on myocardial ischemia-reperfusion injury (MIRI) in mice.Methods:Twenty four C57 MIRI mice were randomly(random number) divided into four groups: SO group, RI group, MSC+RI group, and MSC + RI+ PC61 group. The ratio of Treg were detected by flow cytometry. Serum levels of CK, TNI, BNP, IL-10 and TGF-β were measured by ELISA. The histological changes of myocardium were observed by HE staining. The number of cardiomyocyte apoptosis was measured by TUNEL staining, and the area ratio of myocardial infarction were determined by TTC staining. One-way ANOVA was used to analyze the data.Results:In the MSC + RI group, the ratio of Treg and the levels of IL-10 and TGF-β were the highest, while CK, TNI and BNP were the lowest ( P<0.01) .The number of myocardial apoptotic cells, infarct size and tissue fibrosis were the least ( P<0.01) . Conclusions:MSC can induce the production of Treg, increase the release of anti-inflammatory cytokines IL-10 and TGF-β, and reduce the inflammatory injury after myocardial ischemia-reperfusion.