Abstract: Objective To detect the plasma concentration of Imatinib in Chinese gastrointestinal stromal tumor (GIST) patients, and analyze the relationship between Imatinib plasma concentration and efficacy. Methods We collected 117 plasma samples from 112 GIST patients treated with Imatinib over 28 days. Plasma concentrations of Imatinib were detected using high performance liquid chromatography-mass spectrometry (HPLC-MS/MS). The correlation between Imatinib plasma concentration and efficacy was statistically analyzed. Results The plasma concentrations of Imatinib in high dose (600 mg/day) patients were significantly higher than that in low dose (400 mg/day) patients (P＜0.001). Plasma concentrations in patients treated with Imatinib 1-2 years were higher than that in patients treated less than 1 year (P=0.028). The efficacy was increased along with the increase of plasma concentration of Imatinib, although there was no significant difference between them (P=0.546): the efficacy in low plasma concentration, middle plasma concentration and high plasma concentration was 50%, 67.5% and 66.7%, respectively. Conclusion There were significant correlations between Imatinib plasma concentration and drug dose or time of drug administration; the efficacy of Imatinib was increased along with the increase of plasma concentration.