Objective To investigate the safety and efficacy of umbilical cord blood transplantation (UCBT) in the treatment of metachromatic leukodystrophy (MLD). Methods The clinical data of 3 MLD children treated with unrelated UCBT from April to September 2019 were retrospectively analyzed. Results All the 3 children showed walking disorder, progressive motor function regression, and 2 of them showed mental retardation. Lysosomal arylsulfatase A (ARSA) decreased in all of them. Head MRI of all the 3 children showed abnormal signals of different degrees in the white matter of the brain and they all had compound heterozygous mutations of ARSA gene. All the 3 children were treated with unrelated UCBT, and the pre-treatment regimen was fludarabine + cyclophosphamide + rabbit anti-human thymocyte immunoglobulin + busulfan, and the prevention of graft-versus-host disease (GVHD) was treated with cyclosporine + mycophenolate mofetil + methotrexate. All the 3 children were successfully implanted, and the whole blood of all children reached complete donor chimerism within 1 month after transplantation. Head MRI showed that the progression of brain parenchymal lesions gradually stopped, and ARSA levels gradually returned to normal. All 3 patients developed infection, 2 developed acute GVHD and 1 developed chronic GVHD. After anti-infection and regulatory immunotherapy, they all improved. The last follow-up was in August 2022, and all 3 patients survived. Long-term efficacy and neurological recovery still require long-term follow-up.Conclusion UCBT is a safe and effective treatment to prevent the progression of MLD.