Imatinib mesylate (imatinib) has shown significant effects in patients with chronic myelogenous leukemia. However, hematological toxicity often occurs and requires dosage reduction or discontinuation of imatinib treatment. A patient with chronic myelogenous leukemia in the blastic crisis received granulocyte-colony stimulating factor (G-CSF) simultaneously with imatinib. The patient was continuously treated with imatinib and G-CSF and achieved remission without any severe infection or neutropenia. There are a few reports on the efficacy of combined therapy with G-CSF and imatinib; however, the results in our case are rare suggesting that the use of G-CSF is effective for preventing severe infection. G-CSF enables continuous treatment with high-dose imatinib.