Adenosquamous carcinoma of the duodenal papilla is rare. A 73-year-old man was referred to the Saiseikai-Matsusaka General Hospital with upper abdominal pain and liver dysfunction. Computed tomography (CT) revealed dilatation of the common bile duct (CBD) and intrahepatic bile duct along with a tumor in the distal CBD. The tumor showed enhancement in the arterial phase on contrast-enhanced CT. We performed endoscopic retrograde cholangiopancreatography and noted a red, erosive, bleeding mass in the duodenal papilla with obstruction of the distal CBD, and dilatation of the CBD. Histopathological inspection of a biopsy of the duodenal papilla showed a mixture of adenocarcinoma and squamous cell carcinoma, suggesting the presence of adenosquamous cell carcinoma in the duodenal papilla. Abdominal examinations including positron emission tomography/CT showed no metastasis or lymph node swelling. The clinical stage was determined to be cT2N0M0 Stage IB. We performed subtotal stomach-preserving pancreaticoduodenectomy. Histopathological inspection of the specimen showed a mixture of adenocarcinoma and squamous cell carcinoma, and squamous cell carcinoma accounted for 40% of the tumor. The tumor was defined as pathological Stage IIA, AcbBd, mixed type, med, pT3b, sci, INFb, ly2, v1, ne2, pN1, HM0, PM0, EM0, PV0, A0, R0, pT3N0M0. We suggested adjuvant chemotherapy, but the patient declined adjuvant chemotherapy and wished to be discharged. Abdominal ultrasonography revealed multiple liver metastases 3 months postoperatively. The patient opted for best supportive care and died 9 months postoperatively. Examination of 23 reports of adenosquamous cell carcinoma of the duodenal papilla in Japan suggested that adenosquamous cell carcinoma of the duodenal papilla has a poorer prognosis compared with adenocarcinoma of the duodenal papilla. Some reports have stated that the growth rate is faster for squamous cell carcinoma than for adenocarcinoma. In our case, the tumor was enhanced in the arterial phase and this represents a feature of adenosquamous cell carcinoma of the duodenal papilla. Chemotherapy has not been established for adenosquamous cell carcinoma of the duodenal papilla. We are confident that we can establish effective chemotherapies in the future.