Objective This study was designed to investigate the effect of the pathway of B7/CD28 and CD4 CD25  regulatory T cells on the recipient immunoloregulation in the model of SD to Wistar rat cardiac allotransplantation. The mechanisms of rejection in allotransplantation will be explored in the model.Materials and methods CD4 CD25  regulatory T cells were isolated from Wistar rat splenocytes and peripheral lymphnodes by using magnetic cell sorting system (negative selection and positive selection). The purity of isolated CD4 CD25  regulatory T cells was detected by flow cytometry.Donor(SD rat) and recipient(Wistar rat) were divided randomly into four groups. Group A(no treatment): The heart from SD rat was transplanted into the abdomen of Wistar rat without any pre-treatment; Group B(B7-2 mAb Group ): Tolerance was induced in Wistar rats by injecting 1mg B7-2 mAb in abdomen when doing heterotopic transplantation; Group C (control group): 1x 106 fresh CD4 CD25  regulatory T cells were infused intravenously into the caudal vein of each Wistar rat 1 day before transplantation; Group D (experimental group): the recipients were injected with 1x 106 CD4 CD25  fresh regulatory T cells 1 day before transplantation and 1mg B7-2 mAb on the day of transplantation. The mean survival time (MST) of grafted heart,the content of CD4 CD25  regulatory T cells in peripheral blood,the optical density(OD) of mixed lymphocyte reaction (MLR), the expression of IL-2、TGF-β1 and the pathology were observed.Results (1)MST:Group A: 7.5±1.7d; Group B: 48.3±7.6d; Group C: 68.5±5.6d; Group D: 84.3.6±5.1d.The MST of Group B,Group C and group D were longer than group A, P GroupB ,P >0.05.The MST of Group D > Group C,and P0.05.IL-2 after grafting in group D is lower than that in both of group B and group C, P0.05. In group D, TGF-β1 was strongly expressed on week 1、4 and 6 after grafting, P<0.05. TGF-β1 after grafting in group D is much higher than those in group B、C and P<0.05.Conclusions 1、Injecting B7-2mAb can block the pathway of B7/CD28.Secretion of IL-2 is inhibited, while expression of TGF-β1 is increased. It helps to induce immune tolerance.2、Infusing fresh CD4 CD25  regulatory T cells can precipitate Th1 and Th2 cell respondence to immune deviation.Secretion of IL-2 is inhibited, while expression of TGF-β1 is increased. It helps to induce immune tolerance.3、Injecting B7-2mAb affiliacted with Infusing fresh CD4 CD25  regulatory T cells can induce immune tolerance better in this experiment.4、Injecting B7-2mAb can inhibit the generation of CD4 CD25  regulatory T cells,increase their inhibitory function by TGF-β1.