Abstract： Objective To investigate the expression of tolerance-associated interleukin (IL)-2 mRNA and IL-10 mRNA in rats after allogeneic liver transplantation. Methods The experimental rats were randomly divided into 3 groups : acute rejection model group (group Ⅰ ), CD4+CD25+T cell treatment group (group Ⅱ), donors of the two groups were Wistar while recipients were Spregue-Dawley (SD) rats, and group Ⅲ as control group, both donors and recipients of this group were SD rats, with 12 rats in each group.Splenic lymphocyte of donor in group Ⅱ were injected through vena dorsalis penis 7 days before liver transplantation; equal volume normal saline (NS) were injected in rats of group Ⅰ and Ⅲ. The contents of IL-2 mRNA and IL-10 mRNA in the liver tissue were determined by reverse transcription-polymerase chain reaction (RT-PCR), and the number of lymphocytes in the donor liver was quantified with flow cytometry 7 days after transplantation. Meanwhile the pathologic change in the donor tissue were observed, and the recipients' life span was recorded. Results IL-2 mRNA was expressed strongly in the liver of group Ⅰ , but it was expressed weakly in group Ⅱ , and no expression was detected in the liver of group Ⅲ. IL-10 mRNA was expressed only in group Ⅱ , and the level was high. The rats in group Ⅱ and Ⅲ survived over 30 days,but rats in Ⅰ group had a shorter life (8 - 11 days, both P＜0. 01). There was heavy lymphocytic infiltration in the liver of group Ⅰ ,and was much higher than that of the other groups [group Ⅰ : (14.31±3.41)×106 /g,group Ⅱ : (5.04±1.13)×106 /g, group Ⅲ : (1.55±0. 40)×106 /g, all P＜0. 01], and pathology showed moderate rejection. Rats in group Ⅱ had milder lymphocytic infiltration, and pathology showed no signs of rejection or uncertain rejection, and the ratio of CD4+ T cell and CD4+CD25+ were higher than those of group Ⅰ [(43. 31±8. 07)% vs. (33.65±7.25)% and (11.39±1.92)% vs. (3.05±0.62)%] and group Ⅲ [(43.31±8. 07)% vs. (31.18±6.25)% and (11.39±1.92)% vs. (3.37±0. 72)%, P＜0. 05 or P＜0. 01].In group Ⅲ no lymphocytic infiltration was found, and pathology showed no sign of rejection. Conclusion IL-2 may participate in the immune rejection in allogeneic liver transplantation, but IL-10 plays an important role in CD4+CD25+T cell inducing immune tolerance of allogeneic liver transplantation in the rats.