Objective：To investigate the immunosuppressive effects of leflunomide(Lef) in various organ transplantation models in rats. Methods: Sixty male Lewis rats received othortopic liver, small bowel, kidney and heterotopic heart, pancreas transplantation from ACI rats. Lef in its powder form was suspended in 1%carboxymethylcellulose and was administered at 5 mg．kg－1．d－1 by gavage for 14 d. Results: The survival time of rats in Lef group is significantly longer than the corresponding untreated control group.Besides, 2/6 rats with kidney transplantation and 5/5 rats with liver transplantation were alive over 100 d. Conclusion: Lef as monotherapy in short term treatment can delay acute rejection in heart, pancreas and small bowel transplantation, and lead to long term functional graft survival in kidney and liver transplantation in strong rejecting rat combination. In view of the effect of organ preference by Lef, this agent may be of special benefit to clinical kidney and liver transplantation.