A 75-year-old woman with jaundice was given a diagnosis of bile duct cancer using several imaging modalities. The proximal and middle bile ducts were evaluated as normal by multidetector-row CT and intraductal ultrasonography. However, peroral cholangioscopy (POCS) with narrow band imaging (NBI) clearly revealed the intraepithelial extent of the bile duct cancer from the distal bile duct to the hilar bile duct, which was confirmed by histological examination of the resected specimen. POCS combined with NBI is expected to be useful for determining the resection margin in bile duct cancer cases.