Aplastic anemia preceeding acute leukemia is known as hypoplastic preleukemia, which tends to be more frequently evolved into acute lymphoblastic leukemia, whereas myelodysplastic preleukemia are specific for acute myelocytic leukemia. More than forty cases had been reported in the literatures. Here we report a 11-year-old boy who was initially diagnosed as aplastic anemia and treated with prednisolone and androgen with prompt response terminated into overt acute lymphoblastic leukemia.