A 44-year-old man was referred to our hospital with intermittent abdominal pain. Because distention of fluid- and gas-filled loops of small intestine was proved by X-ray, the patient was diagnosed as having small bowel obstruction. A laparotomy revealed a segmental stenosis in the jejunum, which showed diffuse thickening of the intestinal wall. Some mesenteric lymph nodes were swollen. Pathological examination was defined. We diagnosed diffuse large B-cell lymphoma based on the pathological findings of diffuse transmural infiltration of large lymphoid cells and flow-cytometric analyses. Rituximab was administered as adjuvant therapy at weekly doses of 375 mg/m2. Four cycles were performed every 6 mo and he remained CR. Rituximab may be effective as adjuvant therapy. A 44-year-old man was referred to our hospital with intermittent abdominal pain. Because distention of fluid- and gas-filled loops of small intestine was proved by X-ray, the patient was diagnosed as having small bowel obstruction. A laparotomy revealed Some diagnosed diffuse large B-cell lymphoma based on the pathological findings of diffuse transmural infiltration of large lymphoid cells and Rituximab was administered as adjuvant therapy at weekly doses of 375 mg / m2. Four cycles were performed every 6 months and remained CR. Rituximab may be effective as adjuvant therapy.