Abstract : The case was found first as chronic myelogenous leukemia (CML), based on clinical sign and peripheral blood morphology, but later showed signs of acute lymphoblastic leukemia (ALL). A 35-years-old patient came to the hospital emergency room for the first time, complained of abdomen enlargement since a few months ago. Physical examination showed conjunctival anemia and splenomegaly equal with Schuffner 6, but no lymphadenopathy was found. Laboratory test showed normocytic normochromic anemia, severe leukocytosis, thrombocytopenia, and increased of reticulocytes. Bone marrow puncture (BMP) results were hypercellular, increased granulopoeisis activity, decreased erythropoeisis and megakaryopoeisis, with lymphoblasts were 24% and myeloblasts were 1%. Sokal score calculation was obtained 5.83, classified as high risk of CML. A flowcytometry test found positive of  CD34, CD19, and CD 79a and lead diagnosis to B cell acute lymphoblastic leukemia (B-ALL). The case showed the condition of CML transformed into ALL which obscured the initial diagnosis of CML