Herein is described a mesenteric diffuse large B cell lymphoma (DLBCL) case with a bulky mass which had achieved a complete remission by the combination therapy of a surgical resection and the CHOP chemotherapy with rituximab. A 78 year old man was referred to the Rakuwakai-Otowa Hospital due to a left lower abdominal tumor. Abdominal CT and MRI showed a bowel-like mass in the left lower abdominal cavity. Abdominal US revealed lymph node swellings at the paraaortic region. By the gastro-duodenoscopy, DLBCL of non-Hodgkin's lymphoma was proven at the 2nd portion of the duodenum. On laparotomy, a mass of 8x8cm in size was found at the mesenterium of the ileum, which directly invaded the ileum and the sigmoid mesocolon. A partial resection of the ileum and the sigmoid colon was performed. After the operation, it was determined to be Stage IV DLBCL and the chemotherapy based on the R-CHOP regimen was performed. The regimen was repeated to the 6th course. During the chemotherapy, he was confirmed to have achieved a complete remission. The present case is a rare case in which a Stage IV mesenteric DLBCL with extensive bulky masses had a favorable prognosis. Stage IV mesenteric DLBCLs with extensive bulky masses are thought to be the indication for the combination therapy of surgical resection and multiagent chemotherapy with rituximab.