Objective: To investigate the protective effect of CTLA4Ig in rejection of pancreaticoduodenal transplantation model of rat. Methods: Pancreaticoduodenal transplantion models were established from the donor F344 rats to the Lewis recipients. The models were divided into 2 groups: Group A and B with 12 rats in each group.2 days after transplantation, reciepients in group A were treated with i.p. injection of sailine, and those in group B CTLA4I were injected(200 μg). On day 1,4,7,10after transplantation, the grafts were harvested for histopathological examination. On day 4 after transplantation, the CD4+CD25+Tcells in the grafts were detected by Flow Cytometry. Results: Compared with group A: the degree of the rejection of grafts in group B was lower. The number of CD4+CD25+ T cells of graft was (7.91±1.26)﹪ in group A and (13.81±1.71)﹪ in group B, which had significant difference(P＜0.01). Conclusion: CTLA4Ig could inhibit T cell costimulatory pathway, prevent acute rejection, which might be mediated by increasing the number of CD4+CD25+ regulatory T cells.