Objective To observe the effects of Thymosin α1 （Tα1） on acute rejection after liver transplantation and immune function of T cells. Methods Twenty recipients of liver transplantation due to primary hepatic carcinoma were divided into two groups: Tα1 group (n=10) and control group (n=10). Tα1 group received subcutaneous injection of Tα1 1.6 mg on the first day after liver transplantation and then twice a week for at least one month. Both Tα1 group and control group took same immunodepressants. Core biopsies were carried to compare the incidence rate of acute rejection between Tα1 group and control group. Peripheral T cellular immune function in these two groups was detected on 1 d before, 1 week, 2 weeks and 1 month after transplantation. Results There was not significant difference of incidence rate of acute rejection between Tα1 group and control group (Pgt;0.05). In the Tα1 group, CD4+, CD8+ lymphocyte cell counts and the CD4+/CD8+ ratio were significantly higher than those in the control group in 2 weeks and 1 month after transplantation (P＜0.05). Conclusion Use of Tα1 in recipients who also takes rountine immunosuppressants dose not increase the risk of occurring acute rejection after liver transplantation. Tα1 can significantly increase CD4+, CD8+ counts and CD4+/CD8+ ratio, which shows that Tα1 may improve recipients’ cellular immune function.