Belantamab mafodotin, a B-cell maturation antigen-targeting antibody-drug conjugate (ADC), was investigated in Japanese patients with relapsed/refractory multiple myeloma in Part 1 of the phase I DREAMM-11 study. Patients who had received ≥ 2 prior lines of therapy including a proteasome inhibitor and immunomodulatory agent were eligible. Eight patients received belantamab mafodotin monotherapy at 2.5 mg/kg (n = 4) or 3.4 mg/kg (n = 4) by intravenous infusion every 3 weeks on day 1 of each cycle until disease progression or unacceptable toxicity. Primary objectives were tolerability and safety, and secondary objectives included pharmacokinetics (PK) and efficacy. The most common Grade ≥ 3 adverse event was thrombocytopenia/platelet count decreased (2.5 mg/kg cohort, 100% [4/4]; 3.4 mg/kg cohort, 75% [3/4]), and no dose-limiting toxicities were observed. Ocular events, including keratopathy findings, were observed in most patients (2.5 mg/kg cohort, 100% [4/4]; 3.4 mg/kg cohort, 75% [3/4]) and were managed with dose modifications. All resolved within the study period. Overall response rates were 50% (2/4) in the 2.5 mg/kg cohort and 25% (1/4) in the 3.4 mg/kg cohort. Although PK profiles in Japanese patients varied, individual exposures overlapped with previous results in Western populations. Belantamab mafodotin monotherapy was generally well-tolerated and demonstrated clinical activity at both doses.