Abstract： Several hot questions such as selection of patients and favorable time of transplantation, design of conditioning regimen, monitoring of chimerism and complication of graft versus host disease (GVHD) in allogeneic hematopoietic stem cell transplantation following reduced intensity regimen (RIC-HSCT) as salvage therapy for refractory leukemia are discussed in this article. More and more investigators began to recognize that it was not a fundamental to undergo transplantation in complete remission for patients with refractory leukemia, since it may expend patients' physical status. RIC-HSCT may be substantially considered as a kind of adoptive immunotherapy, so that immunologic attacking targets and the latency of immunoreactian must be considered when making the decision to use, lacking of attacking targets and rapidly growing diseases seemed to be less susceptible to control. Commonly used reduced intensity regimens differed significantly, but it was clear that dose intensity was very important in refractory leukemia. In fact, many investigators used intermediate dosage between criteria of "non-myeloablative" and conventional myeloablative regimens. Complete donor chimerism is the hallmark of engraftment but often delayed in RIC-HSCT. Since sustained complete donor chimerism induced persistent graft-versus-leukemia (GVL) effect play an important role in patients' long-term survival, it was recommended that sensitive techniques (eg. STR-PCR) should be used to analysis chimerism and should be measured more frequently (every 2-4 weeks), and lineage-specific chimerism (eg. T cell) analysis was also recommended. As compared with traditional HSCT, the incidences of acute and chronic GVHD are similar and the onset of GVHD is associated with the GVL effect. Decrease or interruption of immunosuppressive drugs early after transplantation and donor lymphocyte infusion may facilitate transformation to complete donor chimerism, so that it may benefit patients with advanced disease at time of transplantation from avoiding disease relapse in one hand, but may induce GVHD in the other hand.