A 57-year-old man with abdominal discomfort visited our hospital. Abdominal computed tomography (CT) revealed no tumorous lesions. Endoscopic retrograde cholangiography (ERC) revealed a tumorous lesion in the middle bile duct. Peroral cholangioscopy-assisted biopsy was performed, and the lesion was diagnosed as a papillary adenocarcinoma. Extra bile duct resection and regional lymph node dissection were performed; however, residual carcinoma in situ was detected at the ductal margins by intraoperative frozen section analysis. Therefore, external radiation therapy at a dose 50.4 Gy/28 Fr was administered after the operation. No complication due to radiotherapy occurred. The patient remains alive and recurrence -free for more than 7 years after the operation. We report the long-term disease-free survival of a patient with extrahepatic cholangiocarcinoma who was treated with external radiation therapy for positive ductal margins after surgical resection.