Background. To determine the maximum tolerable infusion rate of rituximab, and investigate the safety and feasibility of rapid infusion of rituximab for patients with CD20 positive B-cell lymphomas (CD20+NHL). Patients and Methods. 18 patients with CD20+NHL were registered. This study had six cohorts of administration rate of rituximab. The median age was 56 years (range, 38-79), and five of 18 patients were male. Two patients (11%) with diffuse large B-cell lymphoma were receiving R-CHOP therapy, two (11%) with indolent lymphoma were receiving R-CVP therapy, and 14 (78%) with indolent lymphoma were receiving rituximab as maintenance therapy. Results. A total of 88 cycles of rituximab was administered. Rapid infusion of rituximab was well tolerated, with only one grade 3 leukocytepenia and one grade 4 neutropenia. Four patients (22%) developed grade 1 infusion-related toxicities at the first administration of rituximab. No patient with severe drug-related events was observed. Conclusions. We determined that the maximum tolerable infusion rate of rituximab is 300 mL/h (under 700 mg/h), and confirmed that administration of over 60 minutes is safe and feasible. We recommend rapid administration of rituximab for practice setting in patients with CD20+NHL being treated with rituximab or rituximab-containing chemotherapy. (Clinical trial no. JFCR2009-1027).