Graft-vs.-host disease (GVHD) caused by immunologic activated cells remains a real problem in human allogeneic hematopoetic stem cell transplantation. Mesenchymal stem cells (MSCs) play some important roles on immunomodulatory. We developed a parent-into-F1 model of acute GVHD to evaluate the mechanisms involved in immunological mediated damage and the immunomodulatory effect of the MSCs on GVHD. The recipients, BABL/cxC57BL/6 (H-2(bxd)) F1 mice, received 8.5Gy total-body gamma irradiation ((6)(0)C(O)), then rescued with C57BL/6 (H-2(b)) mice (donors) bone marrow cells and induced acute GVHD by adding donor splenocytes. The MSCs culture-expanded from C57BL/6 (H-2(b)) mice were infused to recipients simultaneity in the experimental group. The severity of GVHD was evaluated by histopathologic examination of target organs including liver, intestine, and claw skin and a clinical manifestation scoring system. We analyzed the distribution of peripheral blood T cell subsets of recipients by flow cytometry and measured the expression of CXCR3 on activated T cells in target organs by immunohistochemistry staining. Our results suggested the tissue damage initiated by GVHD was significantly alleviated in the MSCs treated mice, and the proportion of type 2 T cells in peripheral blood was higher in the MSCs treated mice than in the control group. Although the overall survival rate did not significantly improved in the mice with MSCs infusion, the immunomodulatory effect of MSCs was possibly related to favor type 2 T cell subsets and decrease chemokine receptor CXCR3 expression on activated T cells.