【Abstract】Objective This study was conducted to build experimental model of orthotopic liver transplantation in rat (ROLT) with the character of acute rejection; and to study the effect of cytotoxic T lymphocyte antigen 4 immunoglobulin G (CTLA4Ig) on prevention of rejection and the induction of immune tolerance of ROLT. Methods Build model of Wistar→SD ROLT(performed by the two cuff method) with character of acute rejection.Recipients were injected with CTLA4Ig 75 μg per ROLT into abdominal cavity after 2 days of operation. Contrast was made with no treatment group, the clinical characters, the liver function, the transplantated liver pathologic character and the concentrations of TNFα in serum were observed and measured on postoperative day 7. In treatment group, all above observation were done on postoperative month 4. Above all, determination of the effect of CTLA4Ig on preventing acute rejection and inducing tolerance in ROLT was observed.Results ①Recipients (no treatment group) died one by one within 6th～14th days; pathologic character of rejection in transplantation liver could be found; ② In treatment group, on postoperative day 7 and month 4, no clinical rejection character and no pathologic character of rejection in transplantation liver were found and serum concentration of cytokins related to TNFα found lower than that of contrast group(P＜0.05), and serum concentration of ALT、AST、TBIL、DBIL found lower too(P＜0.05); But serum concentration of TP and Alb was found higher than that of contrast group(P＜0.05). Conclusion ① CTLA4Ig treatment alone inhibits the rejection responce in ROLT. ② CTLA4Ig treatment can Prevent rejection and induce immune tolerance in ROLT model with characters of acute rejection; the serum concentration of cytokins related to TNFα can probably be used as evaluation standard of rejection in ROLT rejection.