Chimeric antigen receptor (CAR) T cells targeting CD19 have achieved breakthroughs in the treatment of hematological malignancies, such as relapsed/refractory non-Hodgkin lymphoma (r/rNHL); however, high rates of treatment failure and recurrence after CAR T-cell therapy are considerable obstacles to overcome. In this study, we designed a series of tandem CARs (TanCARs) and found that TanCAR7 T cells showed dual antigen targeting of CD19 and CD20, as well as formed superior and stable immunological synapse (IS) structures, which may be related to their robust antitumor activity. In an open-label single-arm phase 1/2a trial (NCT03097770), we enrolled 33 patients with r/rNHL; 28 patients received an infusion after conditioning chemotherapy. The primary objective was to evaluate the safety and tolerability of TanCAR7 T cells. Efficacy, progression-free survival, and overall survival were evaluated as secondary objectives. Cytokine release syndrome occurred in 14 patients (50%): 36% had grade 1 or 2 and 14% had grade 3. No cases of CAR T-cell-related encephalopathy syndrome (CRES) of grade 3 or higher were confirmed in any patient. One patient died from a treatment-associated severe pulmonary infection. The overall response rate was 79% (95% confidence interval [CI], 60-92%), and the complete response rate was 71%. The progression-free survival rate at 12 months was 64% (95% CI, 43-79%). In this study, TanCAR7 T cells elicited a potent and durable antitumor response, but not grade 3 or higher CRES, in patients with r/rNHL.