We report a case of intraductal papillary neoplasm of the bile duct(IPNB) that developed in a patient with primary sclerosing cholangitis. A 46-year-old woman was admitted to our hospital with obstructive jaundice. The liver function tests demonstrated increased serum liver enzyme levels. Computed tomography showed dilatation of the intrahepatic bile ducts. Abdominal ultrasonography revealed a highly echoic protruding lesion in the posterior bile duct near the right lobe of the liver. The lesion was suspected to be IPNB, but we were unable to confirm whether it was a carcinoma. A right hepatectomy was performed, and this showed that the dilated bile duct was filled with mucin and contained several yellowish papillary tumors. Histologically, the neoplastic biliary epithelium showed papillary growth in the dilated lumen. The tumor was diagnosed as IPNB, high-grade intraepithelial neoplasia secreting abundant mucin. No recurrence has been detected 3 years after surgery. We report a case of intraductal papillary neoplasm of the bile duct (IPNB) that developed in a patient with primary sclerosing cholangitis. A 46-year-old woman was admitted to our hospital with obstructive jaundice. The liver function tests demonstrated increased serum liver enzyme Levels. Computed tomography showed dilatation of the intrahepatic bile ducts. Abdominal ultrasonography revealed a highly echoic protruding lesion in the posterior bile duct near the right lobe of the liver. The lesion was suspected to be IPNB, but we were unable to confirm whether it was a carcinoma. A right hepatectomy was performed, and this showed that the dilated bile duct was filled with mucin and contained several yellowish papillary tumors. Histologically, the neoplastic biliary epithelium showed papillary growth in the dilated lumen. The tumor was diagnosed as IPNB, high -grade intraepithelial neoplasia secreting abundant mucin. No recurrence has been detected 3 years after surgery.