Background: CT103A is a fully human chimeric antigen receptor T cell product targeting B cell maturation antigen (BCMA). Our previous reports showed a remarkable efficacy and safety of CT103A in patients with relapsed/refractory multiple myeloma (RRMM) at a median follow-up of 394 days. Here, we report the updated safety and efficacy profile in the long-term follow-up. Methods: This trial was a phase 1, single-arm, open-label study conducted in Tongji hospital in China. Eighteen consecutive patients with RRMM were enrolled, who received at least three lines of prior therapies that contain a proteasome inhibitor and an immunomodulatory agent. Lymphodepletion was performed using Fludarabine (30 mg/m 2) and cyclophosphamide (500 mg/m 2) for three consecutive days. CT103A was administered at 1, 3 and 6×10 6 CAR-positive T cells/kg in the dose-escalation phase, and 1×10 6 CAR-positive T cells/kg in the expansion cohort. From one-year post infusion, the response was evaluated every six months according to the IMWG 2016 consensus criteria. Minimal residual disease (MRD) was evaluated in the visits that bone marrow aspiration was performed. The minimum sensitivity of MRD was 10 -5 nucleated cells by standardized flow cytometry. All the adverse events (AEs) during the long-term follow-up were recorded and graded by CTCAE v5.0.