A 56-year-old woman was referred to our hospital with a growing gastric submucosal tumor. An upper endoscopic examination revealed two gastric tumors, an original polypoid tumor and a newly diagnosed superficial tumor. Boring biopsied specimens of the submucosal tumor showed gastric plasmacytoma; however, the other specimens showed no malignancy. Blood diseases were ruled out using various examinations; therefore, we diagnosed the tumor as extramedullary gastric plasmacytoma. The patient underwent laparoscopic distal gastrectomy, and both tumors were thus revealed to be plasmacytomas. We experienced a rare case with two differently shaped extramedullary gastric plasmacytomas without significant morphologic change during the follow-up.