Chronic myeloid leukemia (CML) is a chronic myeloproliferative disease almost always caused by a genetic defect known as the Philadelphia (Ph) chromosome. Ph chromosome is associated with a BCR/ABL fusion gene expressed as an oncoprotein, which is generally considered as the initiator for the chronic phase of CML. Tyrosine kinase inhibitors (TKI) are target-specific therapeutic agents that has successful results for obtaining complete responses for the majority of patients with this disease. Imatinib mesylate has been accepted as standard of care for the newly diagnosed chronic phase patients with CML. Although imatinib mesylate has been successful in most of patients by providing complete hematological and cytogenetical response and also major molecular response, imatinib resistance could be seen in some of the patients detected as loss of the response or never obtained optimal response. The response criteria for CML patients treated with imatinib, definition of the optimal response, suboptimal response and failure were defined and published as ELN recommendations. Dasatinib is approved for imatinib resistant and intolerant CML patients. In this report, we have presented a case with chronic phase CML who lost hematological and cytogenetical response and successfully treated with dasatinib.