Chronic Myelogenous Leukemia (CML) is a myeloproliferative neoplasm that can progress into various conditions. Transformation of CML into Acute Lymphoblastic Leukemia (ALL) is rare. An 8-year-old girl is brought to the hospital because of a fever. physical examination revealed hepatosplenomegaly, the patient had a history of bone marrow morphology examination in 2019 chronic phase CML with blast count <10%. In 2021, an assessment of the bone marrow was carried out again, showing a hypocellular picture, no erythropoiesis cells, and only a few granulopoiesis cells were found, and there were no megakaryocytes. Infiltrating lymphoblasts dominate cells in the bone marrow. The transformation of CML to ALL can occur in 5% of children and 40% of adults. Change can occur due to genetic mutations and inadequate treatment.