We report a case of serous cystadenoma of pancreas causing left-sided portal hypertension and gastric varices. A 68-year-old man was admitted for treatment of a pancreatic body tumor. Contrast-enhanced computed tomography (CT) showed a honeycombed cystic mass. A celiac angiogram showed a hypervascular tumor supplied mainly by a dilated splenic artery and dorsal pancreatic artery. In the venous phase, the patent splenic vein had a large hepatopetal collateral vein via the coronary gastric vein. Upper gastrointestinal endoscopy showed isolated varices of the gastric fundus. We made a preoperative diagnosis of a serous cystic tumor of the pancreas with left-sided portal hypertension and performed distal pancreatectomy with splenectomy. The resected tumor was 8 cm in diameter and had a typical honeycombed microcystic pattern with central stellate scarring. The spleen was not enlarged. Histopathological examination confirmed a diagnosis of serous cystadenoma without any sign of malignancy. Postoperative endoscopy showed disappearance of the gastric varices.