Juvenile myelomonocytic leukemia(JMML) is a rare myeloproliferative disorder of early childhood. It is usually characterized by peripheral monocytosis, increased level of HbF, and hypersensitivity of hematopoietic progenitors to granulocyte-macrophage colony-stimulating factor and hepatosplenomegaly. The pathogenesis of JMML has been associated with deregulated signal transduction and growth factor hypersensitivity. Allogeneic stem cell transplantation is the only curative approach but the roles of pretransplant chemotherapy, conditioning regimen and graft-versus-host disease are still unclear. Graft-versus-leukemia effect may play an essential role because withdrawal of immunosuppressive therapy and donor lymphocyte infusion was successful in the relapsed patients after transplantation.