Acute myeloid leukemia (AML) transformed by myelodysplastic syndrome (MDS) has low complete remission,high risk of relapse,short survival time and poor prognosis.If the patients also with FLT3-ITD positive,the outcome will be worse,and the possibility of survival is very low,even after allogeneic hematopoietic stem cell transplantation (Allo-HSCT).In this paper a 44 year old female patient with FLT3-ITD+ AML-M5,transformed by MDS treated in our department were reported.The patient received chemotherapy with decitabine before and unrelated donor Allo-HSCT,and maintenance therapy of small dose of decitabine after HSCT.The early relapse after transplantation was successfully controlled,and the life of the patient had been over 2 years.