Acute myeloid leukemia (AML) is a heterogeneous disease often associated with poor prognosis. We previously showed that the localization of KIT-D816V at endolysosomes is critical to activate aberrant Akt signaling and Chlorpromazine (CPZ) perturbs the intracellular localization, leading to cell death in AML cells with KIT-D816V. We report that daily administration of CPZ, prescribed for controlling anxiety disorder in patient with AML harboring KIT-D816V, led to a dramatic reduction in AML cells. In vitro and in vivo experiments showed that CPZ inhibited the growth and survival of the patient-derived AML cells, implying potent efficacy of CPZ in AML with KIT-D816V.