A 49-year-old man was diagnosed with pure red cell aplasia (PRCA) based on low reticulocyte count (0.1%) and near absence of erythroblasts in the bone marrow (BM). While a small number of CD20-positive large abnormal cells was observed in the BM, Multiplex PCR confirmed B cell monoclonality. Gallium scintigraphy showed abnormality only in the BM, and we made a diagnosis of PRCA secondary to BM-derived B-cell malignant lymphoma. He was treated with rituximab-combined CHOP therapy with subsequent resolution of both disorders. He was further treated with high dose chemotherapy with auto-PBSCT, sustaining complete remission of the PRCA and lymphoma.