Mucinous adenocarcinoma is a rare histologic type of gastric carcinoma. Most mucinous gastric carcinoma is diagnosed by histology after surgical resection. However, in this report, we preoperatively predicted the type of a tumor (mucinous type) from its characteristic endoscopic finding. An endoscopic examination showed a cauliflower-like mass on the upper body of the posterior wall. At first we could not find the mass because it was covered with a thick mucin-like substance. After gastric lavage and mucin aspiration we found a tumor mass which was surrounded with a characteristic mucin pool. Abdominal CT showed a 6 cm sized-mass connected with the gastric fundus. Total gastrectomy with esophagojejunostomy was performed. The pathology of the tumor proved to be a mucinous adenocarcinoma. (Korean J Gastrointest Endosc 2003;27:3841)