Objective of this study was to evaluate the efficacy and safety of haploidentical or unrelated donor hematopoietic stem cell transplantation (HSCT) for patients with severe aplastic anemia (SAA). Twenty patients with SAA received allogeneic HSCT from haploidentical or unrelated donors (14 from haploidentical donors and 6 from unrelated donors) from November 2005 to May 2011. Conditioning regimen consisted of fludarabine (FLU), cyclophosphamide (Cy) and anti-thymocyte immunoglobulin (ATG). The patients were administrated with G-CSF-primed bone marrow and mobilized peripheral blood as grafts from haploidentical donor or only mobilized peripheral blood from the unrelated donor. The results showed that the median time of neutrophil and platelet engraftment were 14 (11 - 20) d and 17 (13 - 31) d respectively. All patients who achieved engraftment had complete hematologic recovery with complete donor chimerism, except for two patients who developed graft failure in 2 months after transplantation. Four cases developed acute grade IIGVHD. The chronic GVHD occurred in 7 of the 16 evaluable cases (6 limited, 1 extensive). 14 patients got disease-free survival with follow-up to January 2012. The disease-free survival rate was 68.9%. It is concluded that the haploidentical or unrelated donor hematopoietic stem cell transplantation may become a viable therapeutic option for severe aplastic anemia patients who lack suitable human leukocyte antigen-matched donors and fail immunosuppressive therapy.