Extramedullary plasmacytoma is a rare disease in which a neoplastic proliferation of plasma cells originates from the outside of the bone marrow. The jejunum is the most common site of extramedullary plasmacytoma of the gastrointestinal tract and its common complications are intestinal obstruction due to mass, gastrointestinal bleeding, and intussusception. A 68-year-old woman presented with intermittent postprandial abdominal pain, vomiting, and weight loss. Abdomen and pelvis CT revealed diffuse wall thickening of the proximal jejunum. Small bowel series and enteroclysis revealed a short segment stricture of the proximal jejunum. A 2 cm long jejunal stricture was detected on peritoneoscopic surgery. A pathology showed a solid mass beneath the submucosa grossly and malignant plasma cell infiltration microscopically. A immunochemical staining showed monoclonal kappa chain expression. A bone marrow examination showed only mild reactive plasmacytosis. Serum protein electrophoresis, skull and spine X-ray showed no specific abnormality, and urinary Bence Jones protein was negative.