A 7-year-old girl with acute myelogenous leukemia with multilineage dysplasia received unrelated cord blood transplantation but developed hemophagocytic syndrome (HPS) after sepsis with methicillin-resistant coagulase-negative staphylococci before engraftment. Bone marrow aspiration on day 20 revealed a markedly increased number of activated macrophages showing hemophagocytosis. The presence of donor-type chimera in the bone marrow was confirmed at that time. We therefore quickly started immunosuppressive and antibacterial treatment. Although her condition gradually improved, the patient suf-fered graft failure due to HPS. She received peripheral blood stem cell transplantation from her HLA 2-loci-mismatched mother on day 54 and continued in complete remission 12 months after the second transplantation. The results in this case sug-gested that because of fetomaternal microchimerism it may be useful to select an HLA-haploidentical mother as a backup donor for stem cell transplantation.