Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has curative potential against hematological malignancies. However, there are concerns about the associated risk of non-relapse mortality (NRM). We performed a retrospective single-center study to assess changes in outcomes after allo-HSCT and causes of NRM over three 5-year periods. The rates of 2-year NRM and overall survival (OS) were 16% and 59%, respectively. We found a significant decrease in NRM (P<0.001), with 2-year NRM of 26, 14 and 9%, and a significant increase in OS (P=0.005), with 2-year OS of 52%, 58% and 65%, over the three periods (1998-2002, 2003-2007 and 2008-2012), respectively. Of note, a steady improvement was observed in NRM, period by period, among patients aged 50 years or older, patients who underwent HSCT from an unrelated bone marrow donor and patients who underwent HSCT with a reduced-intensity conditioning regimen. Our data showed that the improved NRM can mainly be attributed to a decreased mortality related to infection after starting systemic steroid as GVHD treatment, and a decreased mortality related to organ failure.