Myelodysplastic syndromes (MDS) often transform into acute leukemia (AL-MDS), although its prognostic details have not been examined thoroughly. We retrospectively analyzed the prognosis of 189 AL-MDS patients. Ninety-four patients received best supportive care (BSC), and 94 patients received disease-modifying therapies (DMT) that included chemotherapy (CHT) for 65 patients, allogeneic stem-cell transplantation (allo-SCT) for 21 patients, and other therapies for 8 patients. The median survival time was 142 days. In patients treated with BSC, platelet count alone was an independent prognostic factor. In younger patients treated with DMT (<60 years, N=25), allo-SCT was an independent prognostic factor associated with longer survival. In older patients treated with DMT (≥60 years, N=69), the therapy type did not affect survival, and performance status and MDS-specific comorbidity index were independent prognostic factors.