Objective:To investigate the expression differences of miR-200c, miR-19a and miR-155 in gefitinib sensitive and resistant non-small cell lung cancer (NSCLC) patients, and to analyze the effects of miR-200c, miR-19a and miR-155 expression differences on the prognosis of patients.Methods:From August 1, 2015 to August 1, 2019, 80 patients with stage Ⅲ-Ⅳ NSCLC who were treated with gefitinib in the Fourth Affiliated Hospital of Nanjing Medical University were selected as the research objects. Among them, 36 cases were sensitive to gefitinib as the sensitive group, and 44 cases were resistant to gefitinib as the drug-resistant group. The general data, serum levels of miR-200c, miR-19a and miR-155 were compared between the two groups, and the sensitive factors of gefitinib in NSCLC patients and the correlations between serum miR-200c, miR-19a, miR-155 and clinicopathological characteristics of NSCLC patients were explored. The survival of the patients was analyzed.Results:Compared with the drug-resistant group, the number of smoking cases in the sensitive group was less ( χ2=5.541, P=0.019), the number of clinical stage Ⅲ cases was more ( χ2=8.984, P=0.003), the number of well-differentiated cases was more ( χ2=8.673, P=0.003), the number of patients with lymph node metastasis was less ( χ2=6.082, P=0.014), and the levels of serum miR-200c, miR-19a and miR-155 were higher ( t=7.249, P<0.001; t=8.222, P<0.001; t=10.467, P<0.001). Multivariate logistic regression analysis showed that smoking ( OR=0.355, 95% CI: 0.149-0.845, P<0.001), clinical stage ( OR=0.494, 95% CI: 0.274-0.892, P=0.021), degree of differentiation ( OR=6.062, 95% CI: 3.258-11.279, P=0.013), lymph node metastasis ( OR=0.422, 95% CI: 0.245-0.726, P=0.019), the levels of serum miR-200c ( OR=5.521, 95% CI: 3.126-9.752, P<0.001), miR-19a ( OR=5.384, 95% CI: 2.947-9.836, P<0.001) and miR-155 ( OR=5.325, 95% CI: 3.058-9.274, P<0.001) were all influencing factors of gefitinib sensitivity in NSCLC patients. The levels of serum miR-200c, miR-19a and miR-155 were significantly correlated with clinical stage ( t=3.230, P=0.002, r=-0.578; t=3.188, P=0.002, r=-0.612; t=3.123, P=0.003, r=-0.594), degree of differentiation ( t=2.586, P=0.012, r=0.610; t=4.009, P<0.001, r=0.632; t=4.773, P<0.001, r=0.594) and lymph node metastasis ( t=2.902, P=0.005, r=-0.587; t=3.721, P<0.001, r=-0.629; t=3.391, P=0.001, r=-0.614) of NSCLC patients. Compared with the patients with low levels of serum miR-200c, miR-19a and miR-155, the 1-year survival rates of the patients with high levels of serum miR-200c (63.19% vs. 4.37%, χ2=32.562, P<0.001), miR-19a (61.01% vs. 4.75%, χ2=37.807, P<0.001) and miR-155 (57.82% vs. 0, χ2=44.454, P<0.001) were higher, with statistically significant differences. Conclusion:The levels of serum miR-200c, miR-19a and miR-155 are significantly increased in gefitinib-sensitive NSCLC patients, which are important influencing factors of gefitinib sensitivity, and are closely related to clinicopathological characteristics such as clinical stage, differentiation degree and lymph node metastasis of NSCLC patients, and the prognosis is better in patients with high serum levels.