CHOP therapy combined with rituximab (R-CHOP) is currently a standard chemotherapy for diffuse large B-cell lymphoma (DLBCL). However, relapse is detected despite R-CHOP in approximately 30% of patients. Treatment results should be further improved. Previously, second- and third-generation therapies such as MACOP-B, m-BACOD, and ProMACE-CytaBOM were performed to improve the results of DLBCL treatment. However, dose intensity (DI) enhancement increased treatment-associated toxicity, and the treatment results did not improve. Recently, the entity of the relative dose intensity (RDI) was proposed as an index of the intensity of chemotherapy. In this method, the ratio of actual DI to the DI designed per specific period is numerically evaluated. The purpose of calculating the RDI is to achieve chemotherapy as scheduled while maintaining the DI, and not to improve the DI. Previous studies reported that the maintenance of the RDI during CHOP therapy improved the treatment results. In this paper, we review DI and RDI in studies of DLBCL, and revisit the significance of these indicators.