Objective: To explore the clinical efficacy and safety of unrelated umbilical cord blood transplantation (UCBT) in the treatment of refractory and relapsed acute leukemia (AL) patients. Methods: The clinical data of 22 refractory and relapsed AL patients who were treated with UCBT as salvage therapy from November 2009 to May 2017 were retrospectively analyzed. All patients received a myeloablative conditioning regimen for prevention of graft-versus-host disease (GVHD) with cyclosporine A (CSA)/short course of mycophenolate mofetil (MMF). Results: ①Of 22 patients, 9 cases were male and 13 female. The median age was 23 (15-44) years and median weight of 52.5 (43-82) kg. All patients were transplanted with a median umbilical cord blood nucleated cells of 3.07 (1.71-5.30)×10⁷/kg (by weight), the median CD34⁺ cells was 1.60 (0.63-3.04)×10⁵/kg (by weight). ②The myeloid cumulative implantation rate was 95.5% (95%CI 45.2-99.7%) after transplantation of 42 d, with the median implantation time of 19 (13-27) d. The platelet cumulative implantation rate after transplantation of 120 d was 81.8% (95%CI 54.2-93.6%), the median implantation time of 42 (20-164) d. ③The incidence of Ⅱ-Ⅳ, Ⅲ-Ⅳ aGVHD and the 2 year cumulative incidence of cGVHD were 36.4%, 13.6% and 40.3% respectively. ④ The transplant related mortality (TRM) after transplantation of 180d was 22.7%, 2 year cumulative rate of relapse was 18.7% (95%CI 3.6-42.5%), 2 year disease-free survival rate (DFS) and overall survival rate (OS) were 53.7% and 58.1%, respectively. Conclusion The preliminary results show that the use of UCBT is safe and effective for refractory and relapsed AL patients who fail to respond to conventional chemotherapy.