Abstract Our study aimed to determine the correlation between mean trough Imatinib plasma levels and molecular response in 131 Chronic Myeloid Leukemia (CML) patients. Imatinib plasma levels were also compared in patients who were on Glivec versus those on generic/biosimilar imatinib . Plasma Imatinib trough levels were estimated by high-performance liquid chromatography (HPLC). A receiver operating characteristic curve was constructed to estimate a plasma imatinib threshold level that correlates with a favorable response. Patients were divided into Responders and Non Responders. The mean trough imatinib plasma level in the responders was significantly higher (2.10±1.18µg/ml)/ (3.56±2.0µM) than in the non responders (1.31±0.72µg/ml)/ (2.22±1.22 µM) (p value= 0.001). The area under ROC curve was 0.733, with best sensitivity (51.85%) and specificity (89.42%) at a plasma threshold of 0.988 µg/ml /1.675 µM. There was no significant difference between the mean trough levels of the patients who were on Glivec vs on generic / biosimilar imatinib (p value > 0.05). Trough levels may be a marker for suboptimal response to Imatinib and may identify patients in whom increase of drug dose or change in therapy may be indicated.