A 75-years-old man was diagnosed with a cystic submucosal tumor of the middle body of the stomach and diffuse cystic malformation. Laparoscopic total gastrectomy was performed since a type II c gastric cancer was found at the lower body of the stomach after 1-year follow-up. Histopathological examination revealed mucosal adenocarcinoma with diffuse cystic malformation. Strict observation and appropriate treatment are needed for diffuse cystic malformation because of its significant carcinogenic rate.