We report a case of renal allograft rejection induced by the administration of interferon-alpha for hepatitis type C in a 36-year-old male. In September 1986, renal transplantation from his brother was performed after a 6-month delay because of his liver dysfunction. In October 1992, under the diagnosis of chronic active hepatitis type C, interferon alpha therapy was administered. Although his liver function was normalized during the treatment, proteinuria turned positive after 8 weeks of the therapy. Fourteen weeks after the start of interferon alpha therapy, the serum creatinine level was elevated, which was diagnosed clinically as a rejection reaction. We first discontinued the medication of interferon alpha and administered steroid pulse injection. As the renal disfunction did not respond to our first treatment, we changed mizoribine to azathioprine and added horse antilymphocyte immunoglobulin. Two weeks later, the creatinine level improved from 2.5 mg/dl to 2.0 mg/dl. The pathological findings of the transplanted kidney were acute on chronic type rejection.