Serum concentration of soluble interleukin-2 receptor (sIL-2R) predicts the clinical outcome of patients with aggressive non-Hodgkin's lymphoma treated with the cyclophosphamide, doxorubicin, vincristine, and prednisolone (CHOP) regimen without rituximab. In the present study, we aim to re-assess the prognostic significance of serum sIL-2R for diffuse large B cell lymphoma (DLBCL) patients treated with CHOP plus rituximab and to assess sIL-2R with subtype of DLBCL, such as GCB type and non-GCB type. Two hundred and thirty-three patients with DLBCL were enrolled between December 2002 and March 2008. To evaluate serum levels of sIL-2R, venous blood samples were drawn from patients immediately before initiation of treatment. Serum sIL-2R was determined by sandwich enzyme-linked immunosorbent assay. The 5-year overall survival (OS) rates for patients with sIL-2R levels of ≥2,000 (110 cases) and <2,000 U/mL (123 cases) were 54.2% and 89.0% (P < 0.0001), respectively. Multivariate analysis using the proportional-hazards model revealed that serum sIL-2R (P = 0.0099) and extranodal involvement sites (P = 0.0392) were independent prognostic factors for OS and that clinical stage (P = 0.0168), performance status (P = 0.0181), sIL-2R (P = 0.0232), and LDH (P = 0.0316) were independent prognostic factors for progression-free survival in sIL-2R and every factor of the International Prognostic Index. Serum sIL-2R might be a useful prognostic factor for DLBCL patients in the rituximab era.