OBJECTIVE Although the 2015 World Health Organization Classification reported that histological grading may be helpful in lung cancer management, a widely accepted histological grading system with clearly defined criteria and demonstrable clinical significance has not been developed. We investigated the prognoses of patients with resected non-small cell lung cancer (NSCLC) to identify prognostic factors, especially histological grade. METHODS The medical records of 531 patients between 2010 and 2015 were retrospectively reviewed. Overall survival (OS) curve was plotted using the Kaplan-Meier method. Cox regression analyses were used to evaluate the hazard ratio (HR) with endpoint of OS. RESULTS The 5-year OS rate in groups with histological grade 1, grade 2, and grade 3+4 groups was 95.8%, 85.7%, and 72.1%, respectively (p<0.001). Multivariate analysis identified histological grade and vascular invasion as independent predictors of OS [histological grade: HR=1.533, p=0.002]. CONCLUSIONS Histological grade was an independent prognostic factor of patients resected for all stages of NSCLC.