To study the immunocharacteristics of bone marrow mesenchymal stem cell (MSC) and provide experimental evidence for the potential therapeutic application.MSCs were isolated from rat bone marrow and confirmed by immunophenotype, and the growth dynamic and cell cycle were analyzed. MSCs were cultured with or without 200 U/ml interferon gamma (IFNg) , the expression of PDL-1, CD54, CD40, CD80, CD86, MHC-I, and MHC-II was detected by flow cytometry. MSCs were used as regulatory cells in mixed lymphocyte reaction (MLR), the PDL-1 and CD54 molecules on MSCs were blocked to explore their roles in MLR. The IFN, IL-2, IL-4 and IL-10 molecules in culture supernatant were quantified by ELISA. The homing of MSCs to liver and induction of microchimerism were analyzed after MSCs transplantation.The purity of MSCs was high. The growth curve showed that the first two days were the lag phase; the third, fourth, fifth days were the log phase; the sixth and seventh days were the stationary phase. Flow cytometry indicated that 76.0%+/-2.0% of the MSCs were in G1/G0 phase, 13.0%+/-2.0% in S phase, 10.0%+/-1.7% in G2 and M phase. IFNg treatment led to up-regulation of CD54, PDL-1, MHC-I and MHC-II, however, CD40, CD80 and CD86 were not expressed on MSCs even after IFNg treatment. MSCs inhibited MLR, IFNg treatment enhanced the inhibitory effect of MSCs on MLR. Blocking of PDL-1 or CD54 on MSCs partially alleviated the inhibition effect. There were high levels of IFNg and IL-10, and low level of IL-4 in the culture supernatant of MLR, however, IL-2 was not detected. MSCs can home to the liver and induce formation of microchimerism after transplantation.IFNg treatment enhances the inhibitory effect of MSCs on MLR, PDL-1 and CD54 are key molecules mediating this inhibitory effect. MSC can home to the liver and induce formation of microchimerism after transplantation.