Gefitinib is an essential drug for NSCLC patients harboring EGFR sensitive mutations. The approved dose 250 mg/day is based on limited clinical trials, this research aims to explore the relationship between drug exposure and gefitinib response. C trough of 87 NSCLC patients harboring EGFR sensitive mutations were determined by LC-MS/MS. The median of C trough was 173.9 ng/ml (P25-P75, 130.5-231.2 ng/ml), and cutoff value 200 ng/ml was determined by X-Tile. The PFS between C trough < 200 ng/ml and C trough ≥ 200 ng/ml groups were not significantly different (17.3 VS 14.8 months; p = 0.258). C trough was not significantly associated with rash, diarrhea and hepatotoxicity. Non-smokers enjoyed longer PFS than smokers (18.7 VS 9.3 months; p = 0.025). The results showed that, for NSCLC patients with EGFR sensitive mutations, the PFS in lower trough concentration group were not inferior to that in higher trough concentration group and dose reduction is a rational suggestion for adjustment of dose regimen for aforementioned patients. More clinical trials are warranted to explore the precision dose schedule of gefitinib.