An 83-year-old woman had been suffering from palpitations and fatigue for a month. An annual screening test revealed an increased WBC count so she was referred to our hospital. CBC showed extremely elevated WBC count (186,300/microl), in which the population of blastic eosinophils was over 90%. The eosinophils expressed CD7/13/33/34/DR, and the karyotype demonstrated 47,XX,+8. The fusion gene of FIP1-LP/PDGFRalpha in peripheral blood was negative. As plural effusion due to the underlying disease progressively worsened, she was given prednisolone and hydroxyurea, but the effect was limited. Steroid pulse therapy and imatinib (100 mg/day) were administrated. As a result, a prompt response was observed. The WBC count rapidly decreased, but tumor lysis syndrome led to acute renal failure and disseminated intravasucular coagulation appeared. Supportive therapies such as artificial dialysis and transfusions were conducted, but unfortunately she died because of alveolar hemorrhage.