BACKGROUND : Efficacy and safety profiles of alemtuzumab for relapsing-remitting multiple sclerosis (RRMS) mainly come from Western countries and have not been reported in Asian populations. The aim of this study was to report the efficacy and safety of alemtuzumab for RRMS patients in a Korean population. METHODS : We retrospectively reviewed RRMS patients treated with alemtuzumab. Study outcomes included annualized relapse rate (ARR), expanded disability status scale (EDSS) score, 6-month confirmed disability worsening (CDW), confirmed disability improvement (CDI), MRI lesion activity (new/enlarging T2 hyperintense and gadolinium-enhancing T1 lesions), no evidence of disease activity (NEDA), and adverse events. RESULTS : Nineteen patients were identified and mean follow-up was 1.5 years after alemtuzumab initiation. Mean ARR fell from 1.20 pre-treatment to 0.30 post-treatment (p < 0.001). Mean EDSS score remained stable, with a change from baseline of -0.08 at 1 year. After treatment, 16 patients (84.2%) had freedom from 6-month CDW, 3 (15.8%) had 6-month CDI, 11 (57.9%) had freedom from new/enlarging T2 hyperintense lesions, 13 (68.4%) had freedom from gadolinium-enhancing lesions, and 10 (52.6%) had NEDA. Four patients (21.1%) developed relapses after alemtuzumab therapy. CONCLUSIONS : Alemtuzumab efficacy and safety were similar to that reported previously in Western populations. Severe relapses can occur after alemtuzumab administration.