In China, 1100 ng/mL is used as the recommended threshold for imatinib Cssmin in therapeutic drug monitoring (TDM) for metastatic recurrence/unresectable gastrointestinal stromal tumors (GIST) patients. However, there are few studies on characteristics of imatinib Cssmin for adjuvant therapy after complete resection of GIST and neoadjuvant therapy. Consider individual differences of GIST patients, analysis of imatinib in patients with adjuvant and neoadjuvant treatment using a quantitative ultra-performance liquid chromatography coupled with tandem massspectrometry (UPLC-MS/MS) method was conducted in this study. This developed method showed good selectivity and reliability. 25 blood samples collected from October 2019 to October 2021 in 16 patients with adjuvant therapy and 9 patients with neoadjuvant therapy were determined. In the neoadjuvant treatment group, all patients initially received 400 mg/d imatinib. The range of the imatinib steady-state plasma concentration (Cssmin) was 1083-4722 ng/mL. In the adjuvant treatment group, the imatinib Cssmin was in the range of 584-2692 ng/mL after patients given at a dosage of 200, 300, 400 and 600 mg/d. There is no statistical difference in Cssmin between two groups after receiving 400 mg/d imatinib (p=0.402). Among all patients given 400 mg/d imatinib, the Cssmin was significantly correlated with gender (P=0.016).