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Background and objective Despite undergoing curative resection, the 5-year survival rate for stage III non-small cell lung cancer (NSCLC) patients is less than 25%. There is a need for biomarkers for prediction of survival and guiding individual therapy. MiR-155 is one of most commonly upregulated miRNAs in malignancies, and regulates multiple pro-oncogenic pathways. We aimed to investigate the prognostic impact of miR-155 in resected stage III NSCLC patients. Methods Tumor formalin-fixed, paraffin-embedded (FFPE) from 162 resected stage III NSCLC patients were collected. Total RNA including miRNA was extracted, and qRT-PCR was used to determine the expression of miR-155. Results Spearman rank correlation test showed a positive correlation between miR-155 expression and nodal status (r=0.169, P=0.032). MiR-155 expression had a significant prognostic impact in the total cohort (P<0.001), in squamous cell carcinomas (P=0.002) and in adenocarcinomas (P=0.003). In N0-1 subgroup, miR-155 expression did not have a significant prognostic on overall survival in univariate analysis (P=0.319). In N2 subgroup, miR-155 had a negative prognostic effect on OS in univariate analysis (P<0.001). Cox regression analysis revealed that miR-155 expression was unfavorable prognostic factors of OS (RR=2.311, 95%CI: 1.479-3.611, P<0.001). Conclusion High expression of miR-155 represents a valuable marker of poor clinical outcomes in patients with stage III NSCLC.