A submucosal gastric adenocarcinoma, especially the signet ring cell type, is rare. The histologic evaluation techniques for this lesion has not been established; however, histologic confirmation is very important for decision of treatment method. Here, we report a 57-year-old man with a 12-cm gastric submucosal signet ring cell type adenocarcinoma, diagnosed by an endoscopic ultrasound-guided Trucut biopsy and immunochemical studies. This case suggests that the endoscopic ultrasound-guided Trucut biopsy might be a useful diagnostic method in cases of gastric adenocarcinoma with features of gastrointestinal stromal tumor.