An 82-year-old male with jaundice was referred to our hospital for a detailed examination. The computed tomography (CT) examination detected an enhanced mass lesion of the distal bile duct. Endoscopic retrograde cholangiography showed a filling defect corresponding to the CT findings. Simultaneously, a forceps biopsy and an endoscopic retrograde biliary drainage were performed. We performed pancreatoduodenectomy, and adenocarcinoma was pathologically proven. The histopathological finding of the resected specimen was a mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN) composed of large cell neuroendocrine carcinoma and well-differentiated adenocarcinoma. Although pathological R0 resection was achieved, liver metastasis was observed 6 months after the operation. Although neuroendocrine carcinoma (NEC) rarely develops in the bile duct, it manifests a higher degree of malignancy than other ordinary bile duct adenocarcinomas. Further investigation is needed to choose an appropriate treatment.