Introduction. Chronic myeloid leukemia (CML) ranks third among hematological malignancies in Vietnam. Imatinib has become the standard therapy for CML patients in Vietnam since 2009. Materials and methods. A phase IV clinical study for 1 st line imatinib treatment of CML patients, carried out in 121 CML patients treated in NIHBT and receiving imatinib 400 mg/daily from 2010 to 2014. Results. Cumulative CCyR and CMR were achieved in 82 (67.8%) and 80 (66.1%) of patients, respectively. There was a correlation between the time interval (from CML diagnosis to initiating imatinib treatment) and both complete cytogenetic (OR 0.158; p = 0.001) and molecular (OR 0.263; p = 0.018) responses. The analysis demonstrated that imatinib treatment minimized the prognostic impact of previously established prognostic factors in CML. The 3-year PFS and OS rates were 114 (94.6%) and 118 (97.5%), respectively. Hematologic adverse effects were mild with 1st and 2nd grades anemia, granulocytopenia and thrombocytopenia found in 17 (14%), 27 (22.3%) and 29 (23.9%) patients, respectively. The most commonly non hematologic adverse effects occurred in 1st year of followup including periorbital edema, nausea, musculoskeletal pain, and rash.