Introduction: Chronic myelogenous leukemia)CML) is a pluripotential stem cell disease defined by the consistent presence of Philadelphia(Ph1) chromosome, in more than 95% of patients. In chronic phase of CML the Functional abnormalities of neutrophils are mild, this functional abnormality possibly because these neutrophils produced from abnormal stem cell. Nitro blue tetrazolium (NBT) dye reduction test a semiquantitative method that test the defects related to oxidative burst and superoxide generation. The aims of the study: To evaluate the phagocytic function of neutrophils by NBT test in normal control and compare it to that of CML patients after imatinib mesylate therapy, to correlate between the absolute number of neutrophils and the percentage of NBT positive neutrophils in CML patients after imatinib mesylate and to find out if there is any correlation between the percentage of NBT positive neutrophils and the percentage of (Ph1) positive cells. Patients, material and methods: Fifty CML patients were included in this study all of them were on imatinib mesylate therapy. Group 1: thirty six patients were not in complete cytogenetic remission .Group 2: fourteen patients were in complete cytogenetic remission .Control group: Thirty apparantly healthy, medication free volunteers matched for age and sex. The Nitro blue tetrazolium dye reduction test was performed by slide method, blood film and complete blood count were also performed . Results: The patient ages were ranged from 15 to 77 years with mean age of 45.3 ± 14.9, with male to female ratio of 1.43:1. The NBT percentages in control group were ranged from 3 to 9 with mean percentage of 5.8 ±1.6, in group 1 patients were ranged from 0 to4 with mean percentage of 1.28±1.2, while in group 2 were ranged from3 to 6 with mean percentage of 4.46±1.There was a significant difference between the control group and group 1 patient (p=0.000) while there was no significant deference between control group and group 2 patients (p=0.06).There was no significant correlation between the absolute neutrophils count and the percentage of NBT positive neutrophils in both groups of patients (1and 2) with p value of 0.23 and 0.1 respectively. In 26 patients the results of FIHS showed different percentage of cells positive for (ph1) chromosome ranged from 4 to 90 % with average of 48.3% and there was a significant inverse correlation between the percentage of NBT positive neutrophils and the percentage of cells containing (Ph1) chromosome at the 0.01 level (Pearson Correlation =-0.769) In conclusion: the neutrophils function in CML patients after therapy varies according to (Ph1) chromosome conversion and complete cytogenetic remission is associated with normal neutrophils function while the presence of Ph1 chromosome positive cells associated with defective neutrophils phagocytic activity