A 70-year-old man was admitted to our hospital because a mass was incidentally found in the body of the pancreas. The mass was suspected to be serous cystadenoma from the findings of abdominal enhanced computed tomography, magnetic resonance imaging and endoscopic ultrasonography. In addition, another solid mass was detected in the pancreatic head on imaging tests. Magnetic resonance cholangiopancreatography and endoscopic retrograde cholangiopancreatography showed stenosis both of the main pancreatic duct at the head and bile duct, but the brushing cytology of the bile duct at ERCP showed no malignant cells. However, the findings of several examinations strongly suggested the coexistence of a serous cystadenoma and a pancreatic cancer, therefore we conducted spleen-preserving total pancreatectomy, and the pathological findings of the resected specimen showed serous cystadenoma coexistence with pancreatic adenosquamous carcinoma.