A 78-year-old man presented to our hospital with fever and brownish urine. Upon thorough examination, a diagnosis of obstructive jaundice and acute cholangitis associated with a lower bile duct tumor was made. Endoscopic retrograde cholangiopancreatography revealed entire circumferential stenosis of the lower bile duct. Examination of a transpapillary biopsy specimen of the lesion suggested adenosquamous carcinoma. The patient underwent subtotal stomach-preserving pancreaticoduodenectomy. Histopathological examination revealed adenocarcinoma of the lower bile duct and squamous cell carcinoma components;a case of adenosquamous carcinoma was accordingly diagnosed. The lower bile duct tumor directly extended into the pancreatic parenchyma for approximately 1mm. We performed radical surgery and administered adjuvant chemotherapy with gemcitabine because of advanced neural invasion after consulting with the patient. There was no sign of recurrence 46 months after surgery. As adenosquamous carcinoma of the extrahepatic bile duct is rare, it is difficult to preoperatively diagnose the condition. Only a few cases have been reported till date.