Objective　To observe the change in sensitivity of human lung adenocarcinoma A549 cells to gefitinib after up-regulation of mir-7 expression and its underlying mechanism. Methods　The logarithmic growth phase A549 cells were harvested and randomly divided into 4 groups: normal control group (NC group), transfection group (mir-7 group), gefitinib group (G group), and G+mir-7 group (A549 cells were treated with gefitinib after mir-7 transfection). The MTT assay was used to determine the 50% inhibitory concentration (IC50) of gefitinib for A549 cells. Real-time PCR and Western blot were used to determine the mRNA and protein expression of epidermal growth factor receptor (EGFR), insulin-like growth factor 1 receptor (IGF-1R), Raf1 and extracellular signal-regulated kinase (ERK). Results　The IC50 of gefitinib to A549 cells was significantly lower in G+mir-7 group (8.57±0.61μmol/L) than in gefitinib group (15.63±0.82μmol/L, P<0.01). The results of real-time PCR and Western blot showed that the mRNA and protein expressions of EGFR, IGF-1R, Raf1 and ERK were significantly lower in G+mir-7 group than in NC group, mir-7 group and gefitinib group (P<0.01). Conclusion　The up-regulation of mir-7 expression may enhance the sensitivity of A549 cells to gefitinib, and its mechanism may be related to the inhibitory effect of mir-7 on signal pathway of EGFR and IGF-1R.