This study was purposed to investigate the effects and mechanism of transforming growth factor beta (TGF-beta) on acute graft-versus-host disease (aGVHD) after allogeneic bone marrow transplantation (allo-BMT). The recipients were male BABL/c mice, while the donors were male C57BL/6 mice. The murine model of aGVHD had been established by allo-BMT with donor derived T cells. Experiment was divided into four groups: control group, radiation control group, transplantation control group and TGF-beta treated group. Mice in TGF-beta treated group were daily subcutaneously injected TGF-beta1 (1 microg/kg) in two days before transplantation until seven days after it. The results showed that the survival time of mice in TGF-beta treated group was significantly longer than that in transplantation control group, and the aGVHD pathological changes in TGF-beta treated group were milder than that in transplantation control group. At seven days after transplantation, the level of IL-2 in TGF-beta treated group was significantly higher than that in control group, but significantly lower than that in transplantation control group. The level of IL-10 in TGF-beta treated group was significantly higher than that in transplantation control group, but the level of IL-10 in transplantation control group was significantly lower than that in other groups. It is concluded that TGF-beta may alleviate or suppress lethal aGVHD, and elevate the survival rate after allo-BMT in murine model. Accommodating of the Th1 and Th2 cytokine levels is the possible mechanism of TGF-beta preventing lethal aGVHD.