We report here the preliminary results of allogeneic hematopoietic stem cell transplantation with mesenchymal stem cells (MSCs) for 6 cases of severe aplastic anemia. The patients ranged in age from 3 to 16 years, and the median time from diagnosis to transplantation was 32 months (range: 3-156 months). The conditioning regimens consisted of fludarabine, cyclophosphamide, and antithymocyte globulin with or without busulfan. Graft-versus-host disease (GvHD) was prevented by the administration of cyclosporine A, methotrexate, and mycophenolate mofetil, with or without anti-CD25 monoclonal antibody. The grafts were granulocyte colony-stimulating factor-mobilized bone marrow and peripheral blood from HLA antigen-haploidentical donors (3 cases) or peripheral blood only from unrelated HLA antigen-identical donors (3 cases). MSCs were intravenously injected at a median dose of 1.43 × 10(6)/kg (range: 0.85-2.5 × 10(6)/kg). The mean time for neutrophil and platelet recovery was 12.3 and 13.8 days, respectively. Acute GvHD grade I and II developed in 2 cases, and no chronic GvHD was documented. All patients were alive and transfusion independent at a median follow-up of 15 months (range: 6-29 months). Our report suggests that cotransplantation of allogeneic hematopoietic stem cells and MSCs might provide an opportunity for therapy for children with severe aplastic anemia.