A plasmacytoma is a discrete, solitary mass of neoplastic monoclonal plasma cells in either bone or extramedullary soft tissue. Extramedullary plasmacytomoa is a plasma cell neoplasm that presents as a solitary lesion in the soft tissue, most EMPs are commonly involves nasopharynx or upper respiratory tract. Involvement of the gastrointestinal tract occurs in approximatly 10% of cases. but, isolated primary plasmacytoma of stomach is extremly rare. We present a case of 78 year-old female who complained epigastric pain. Ulcerative lesion in antrum was found at Endoscopy, and biopsy finding was chronic gastiritis without Helicobacter pylori colonization. Patient underwent gastric ulcer therapy included Proton pump inhibitor. 1 month later, follow up endoscopy was done, and the ulcer lesion was unchanged, repeated biopsy revealed chronic inflammation without Helicobacter pylori colinization, too. She was performed other proton pump inhibitor with Heliobacter pylori eradication. 2 month later, on follow-up endoscopy, despite of an appropriate and sufficient medical therapy, endoscopic finding had no interval change and repeated biopsy showed dense lymphoplasmacytic proliferation, Immunohistochemical staining for lambda light chain was positive, Ig H rearrangement showed monoclonal gammopathy. She had no evidance of bone marrow involvement of maligant lymphoma. We concluded as primary gastric plasmacytoma. Plasmacytoma is known to occur in extra osseous sites. Primary gastric plasmacytoma, however, is a rare clinical case. Primary gastric plasmacytoma may have varying clinical presentations that may mimic gastric ulcer or tuberculosis or inflammatory bowel disease. Although these cases are rare, treating physician as well as radiologist, and pathologist should be aware of this entity.