<p>We herein report an 80-year-old man diagnosed with immunoproliferative small intestine disease (IPSID) via small bowel endoscopy with a biopsy. He developed persistent diarrhea and subsequently presented with hypoproteinemia and moderate anemia. Transanal double-balloon endoscopy showed prominent villous edema in the middle and lower ileum, while a histological examination showed high lymphocyte/plasma cell infiltration in the mucosal layer. Furthermore, an immunostaining analysis showed that CD3 and CD20 were partially positive, while CD138 was diffusely positive. Immunoglobulin A positivity was also observed. He was diagnosed with IPSID and received a nutritional agent and minocycline. After three months, the patients' symptoms improved. </p>