Allogeneic hematopoietic stem cell transplantation(HSCT) is a curative therapy against a variety of hematological disorders. However, its application has been limited to younger patients without organ dysfunctions due to transplant-related toxicities. Recently, non-myeloablative stem cell transplantation(NST) or reduced-intensity stem cell transplantation(RIST) has been developed as a less toxic HSCT, which enables the application of HSCT to patients of advanced age or with organ dysfunction. The anti-leukemia effect mainly depends on the graft-versus-leukemia(GVL) effect. Chronic myelogenous leukemia(CML) has been known to be one of the best targets for GVL effect, supported by the observation of durable molecular remission after donor lymphocyte infusion for relapse after HSCT. RIST could be a promising treatment modality for patients with CML.