A 60-year-old woman with primary sclerosing cholangitis (PSC) and high levels of ALP, gamma-GTP, and DUPAN-2 was admitted to our institution for examination. The patient did not have ulcerative colitis or pancreatic intraductal papillary mucinous neoplasm. Imaging studies revealed atypical dilation of bile ducts in the left lobe of the liver. Repeated cytologic examinations of the bile showed atypical cells consistent with adenocarcinoma. The patient underwent extended resection of the left lobe of the liver and was found to have intraductal papillary carcinoma with associated mucin-producing bile duct carcinoma. This carcinoma fills dilated bile duct lumens with mucin. This tumor differs morphologically from typical cholangiocarcinoma, which is usually seen in the late stages of PSC. Just one case of mucin-producing bile duct carcinoma arising from PSC has been reported worldwide. The patient has had no signs of recurrence after 27 months. Patients with mucin-producing bile duct carcinoma, as in the case of its pancreatic counterpart, may have a better prognosis and a higher survival rate than patients with typical cholangiocarcinomas.