Follicular lymphoma (FL) commonly recurs and is difficult to cure. Obinutuzumab is a humanized glycoengineered type II anti-CD20 antibody with a mode of action that includes induction of antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and direct cell death. There is no evidence on the effectiveness of re-treatment with obinutuzumab in patients with prior obinutuzumab treatment. Using obinutuzumab-induced-direct-cell-death-resistant cells, we investigated the efficacy of obinutuzumab re-treatment in combination with chemotherapeutic agents used in FL treatment. Human non-Hodgkin lymphoma (NHL) SU-DHL-4 cells were sustainably exposed to obinutuzumab in vitro, and seventeen resistant clones expressing CD20 and showing 100-fold higher IC50 of obinutuzumab than parental cells were established. The growth inhibition effect of obinutuzumab in combination with bendamustine, 4-hydroperoxy-cyclophosphamide, doxorubicin, vincristine, or prednisolone was estimated using an interaction index based on the Bliss independence model. For each clone, there were various combinations of obinutuzumab and chemotherapeutic agents that showed supra-additive effects. Obinutuzumab combined with doxorubicin enhanced caspase-dependent apoptosis and growth inhibition effect. Obinutuzumab combined with prednisolone enhanced DNA fragmentation and G0/G1 arrest. These combinations also had an antitumor effect in mouse xenograft models. Our results indicate that re-treatment with obinutuzumab, when it is combined with chemotherapeutic agents, is effective in the CD20-positive obinutuzumab-induced-direct-cell-death-resistant cells.