Allogenic hematopoietic stem cell transplantation is one of the effective therapy for several hematologic malignancies. Transplantation preparative regimen is designed to eradicate the patient's underlying disease and immunosuppress the patient adequately to prevent rejection of donor's hematopoietic stem cells. so, Conventional myeloablative preparative regimens with high-dose chemotherapy or radiotherapy are related to high rate of morbidity and mortality. however, It has become clear that the high-dose therapy dose not eradicate the malignancy in some patients, and that the therapeutic benefit of allogenic transplantation is largely related to graft-versus-leukemia/graft-versus-tumor (GVL/GVT) effect. An new approach is to utilize less toxic, nonmyeloablative preparative regimens to achieve engraftment and allow GVL/GVT effects to developed. This strategy reduces the risk of treatment-related mortality and allows transplantation for elderly and those with comorbidities that preclude high-dose chemoradiotherapy.