Abstract: Objective To evaluate significance of the quantification of bcr-abl mRNA in diagnosis and therapy of chronic myeloid leukemia (CML),essentiality significance for monitoring minimal residual disease. Methods Bcr-abl mRNA of 518 CML patients were detected using real-time PCR. Results Expression of bcr-abl mRNA was gradually increased among blastic phase (BP) (12.6 %),accelerated phase (AP) (25.4 %) and chronic phase (CP) (57.2 %) (P<0.05). Quantification of bcr-abl mRNA was cut down gradually after allotransplantation in the patients and becomes normal after treatment for 6 months. But quantification of bcr-abl mRNA inpatients treated with imatinib mesylate became normal after 12 months. Conclusion Real-time PCR was reliable and can be used for diagnosis,monitoring the treatment outcome,detecting the minimal residual disease,and predicting blast crisis.