Abstract： Objective To investigate the effects of T. gondii soluble tachyzoite antigen (STAgs) on the survival time of mouse heart allograft and the possible mechanism. Methods The STAgs were prepared by pulverizing T. gondii tachyzoite with ultrasound on ice. Cervical heterotopic heart transplantations were done by using Balb/c mice as donors, and C57BL/6 mice as recipients.The recipients were classified randomly into three groups: syngeneic group, acute rejection group and STAgs-treated group. The recipients in acute rejection group and STAgs-treated group were injected subcutaneously with 0. 1 ml PBS and 0. 1 ml (5 μg) STAgs at the 4th day before transplantation respectively, and those in syngeneic group were not subjected to any treatment. The grafts were observed daily by cervical palpation, and the total cessation of cardiac contraction was defined as the endpoint. The heart allografts were harvested at the 7th day after transplantation for pathological examination and immunohistochemical staining for CD4+ T, CD8+ T. Results The recipients in syngeneic group were all alive at the 100th day after transplantation. The average survival time in acute rejection group and STAgs-treated group was (6.7± 0.5) days and (70.8± 3.5) days,respectively (P＜0.05). HE staining showed that the rejection on the 7th day after transplantation in syngeneic group, acute rejection group and STAgs-treated group was fallen into 0 degree, Ⅲ-Ⅳ degree and 0- Ⅰ degree, respectively. Immunohistochemical staining revealed that the CD4+ T and CD8+T were markedly down-regulated in STAgs-treated group as compared with those in acute rejection group. Conclusion T. gondii STAgs can significantly prolong the survival time of mouse heart allograft and inhibit the rejection probably by changing the ratio of TH1/TH2, or inhibiting the effect of dendritic cells by inducing the lipoxin A4.