A 66-year-old-female was admitted to our hospital with an intra-abdominal tumor. Contrast enhanced CT demonstrated a non-enhancing cystic tumor measuring 6 cm in diameter adjacent to the pancreatic body, stomach and left lateral segment of the liver. EUS showed a mass without blood flow in the pancreatic body, based on which we suspected a cystic lesion of the pancreas. Laparoscopic surgery was performed. A smooth-margined spherical mass was found arising from the anterior wall of the lesser curvature of the stomach at the cardia, and not from the pancreas. We performed local resection of the stomach . Histological examination revealed that the cyst arose from the muscularis propria layer, and that the inner surface of the cyst was partially covered with ciliated columnar epithelium. Therefore, we made the final diagnosis of duplication of the stomach.