Graft dysfunction mimicking autoimmune hepatitis rarely develops after liver transplantation for nonautoimmune disease. The mechanism(s) and causes of de novo autoimmune hepatitis are unknown. We examined autoantibodies serially in a patient with de novo autoimmune hepatitis and in patients without de novo autoimmune hepatitis after liver transplantation. Anticytokeratin 8/18 antibodies were detected in the first patient's sera after the onset of de novo autoimmune hepatitis, whereas other patients without de novo autoimmune hepatitis were seronegative throughout the follow-up period even with acute cellular rejection or other cause of liver dysfunction. In conclusion, the changes in cytokeratin 8/18 in hepatocytes might be one of the sources of pathogenesis of de novo autoimmune hepatitis after liver transplantation.