OBJECTIVE To investigate the correlation of the serum minimal concentrations (Cmins) of nilotinib(NIL) with the clinical efficacy and adverse events (AEs) in CML patients. METHODS A total of 54 patients were divided into two groups according to the dosage of nilotinib. 44 cases received dose of 600-800 mg/d were classified as group A; while 10 cases received dose of 400 mg/d as group B. The Cmins of nilotinib were determmined by liquid chromatography-tandem mass spectrometry. RESULTS Median Cmins of nilotinib in 54 patients was 1.71 (0.52-5.93) µg/ml. Cmins of nilotinib in group A and group B were 2.09± 1.21 µg/ml and 0.94± 0.27 µg/ml respectively, Cmins of group A was significantly higher than that of group B (P=0.001). In group A, 24 out of 44 cases obtained major molecular response (MMR) in 12 months, while 20 cases did not reach MMR in 12 months; the serum drug concentrations were 1.70± 0.75 µg/ml and 2.03± 0.82 µg/ml respectively, without statistically significant differences between these 2 subgroups(P=0.154). However, Cmins of nilotinib in patients with III-IV grade of adverse events were significantly higher than those in patients with 0-II grade of adverse events (3.09± 1.76 µg/ml vs 1.76± 0.68 µg/ml)(P=0.018). There was no statistic diffence in Cmins of nilotinib with MMR in 12 months of group A MMR 1.15± 0.27 µg/ml vs no MMR 0.83± 0.24 µg/ml(P=0.051). The MMR rate at 12 months in group A was 54.5%(24/44) and that in group B was 40%(4/10) (P=0.494). But the incidence of grade III-IV adverse events in group A was 29.5%(13/44), which was significantly higher than that of group B[0/10(0%)]. CONCLUSIONS Cmins of nilotinib shows significant individual differences. The Cmins of nilotinib relate with the dosage and grade III-IV of adverse events. The lower dose of nilotinib may maintain a good therapeutic effect and significantly reduce the adverse events.