Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin lymphoma. The present study assessed retrospectively the clinical significance of the serum soluble interleukin-2 receptor (sIL-2R) level in patients with advanced DLBCL. Twenty-one patients (age; range, 56–87, median, 73-year old, 14 males/7 females) were newly diagnosed as having advanced DLBCL (stages III and IV) based on pathological findings of the biopsy specimen and by using computed tomography and positron emission tomography between 2006 and 2009. All the patients received 6–8 cycles of the combination of rituximab with CHOP (cyclophosphamide, doxorubicin, vincristine and prednisolone) (R-CHOP) or THP-COP (pirarubicin, cyclophosphamide, vincristine and prednisolone) (R-THP-COP) and attained complete response at the end of the treatment. The follow-up period ranged between 12 and 73 months with the median of 37 months. The serum sIL-2R levels (normal range, 144–518 U/ml) were determined at least before and after the second and the sixth cycles of the chemotherapy were carried out. Although all the patients reached complete remission, six patients experienced the disease relapse within 1 year from the initiation of the treatment. sIL-2R levels before the chemotherapy ranged from 416 to 21300 U/ml (median 2609 U/ml). sIL-2R levels after the second cycle of the chemotherapy ranged from 276 to 1980 U/ml (median 675 U/ml). sIL-2R levels after the sixth cycle of the chemotherapy ranged from 364 to 822 U/ml (median 548 U/ml). The early relapse was significantly associated with the high sIL-2R levels at the sixth cycle of the treatment, while the sIL-2R levels were low in the patients with the durable remission. sIL-2R levels at the disease onset or after the second cycle of the treatment were not correlated to the duration of the remission. Thus, the present study suggested that the sIL-2R levels after the sixth cycle of the chemotherapy might predict the early relapse in patients with advanced DLBCL.