Primary Objective is to determine the efficacy, as measured by overall response rate on the basis of Revised Response Criteria for Malignant Lymphoma, of SyB L-0501 at 120 mg/m^2/day on Day 2 and Day 3 in combination with rituximab at 375 mg/m^2 on day 1 of each 21-day cycle in patients with recurrent/relapsed diffuse large B-cell lymphoma.