A 70-year-old man was admitted to our hospital with fever, generalized lymphadenopathy and hypoxia in October 2009. Blood examination demonstrated leukocytosis, anemia, thrombocytopenia and hyper γ-globulinemia. Peripheral blood and bone marrow smear showed marked plasma cell proliferation mimicking plasma cell leukemia. However, flow cytometric analysis showed that plasma cells were of polyclonal origin and M-protein was not detected by immunofixation of serum protein. Elevations of soluble interleukin 2 receptor and serum IL-6 were observed. A heavy Epstein-Barr viral load was detected in serum by real-time PCR. Biopsy was obtained from the right inguinal lymph node. The pathological diagnosis was angioimmunoblastic T-cell lymphoma (AITL) and rearrangement of the T-cell receptor Cβ1 gene was detected. The patient was treated with CHOP therapy, and all clinical manifestations, including fever, lymphadenopathy, anemia, thrombocytopenia, hyper γ-globulinemia, plasmacytosis and hypoxia, were improved. Only a few reported cases have demonstrated AITL with marked polyclonal plasmacytosis. Although pathological mechanisms of plasmacytosis in AITL patients have not been fully elucidated, it is suggested that IL-6 and IL-10 were involved in its pathogenesis in the present case.