Autoimmune pancreatitis (AIP) is characterized by pancreatic manifestations of IgG4-related disease. Malignancies in patients with AIP have been reported, but carcinoma of the bile duct is extremely rare. We report a patient with IgG4-related AIP who developed cholangiocarcinoma after 8 years of steroid treatment. A 76-year-old male presented with fever (37.8°C) due to biliary obstruction and cholangitis. He had been treated with steroids for 8 years to control inflammation due to IgG4-related AIP. During 8 years of treatment, hepatobiliary enzyme levels were well controlled within their normal range, but serum IgG4 levels remained elevated. A computed tomography scan showed intrahepatic bile duct dilatation. Magnetic resonance cholangiopancreatography showed obstructive changes at the junction of the cystic and common ducts. To relieve biliary obstruction, endoscopic bile duct drainage using a nasobiliary tube was performed, and cytology was Class IV. Aorto-caval lymph node enlargement was found at laparotomy, intraoperatively diagnosed as adenocarcinoma, and resection was abandoned. He died 4 months postoperatively. We report a patient with IgG4-related AIP complicated by cholangiocarcinoma which developed after 8 years of steroid treatment. Even if hepatobiliary markers are well controlled, periodic follow-up with imaging studies may facilitate detection of an early cholangiocarcinoma.