Objective <p>Long-term prognosis in patients with early-stage non-small cell lung cancer (NSCLC) achieving 5-year postoperative recurrence-free survival (RFS) has been examined in previous studies. However, no prognostic factors have been identified that contribute to the management of long-term NSCLC survivors. Therefore, this study aims to investigate the factors affecting long-term prognosis, with a focus on the percent predicted diffusing capacity of the lung for carbon monoxide divided by alveolar volume (%DLCO/VA).</p> Methods <p>A retrospective analysis was performed on 642 patients with stage I NSCLC who achieved a 5-year postoperative RFS. Patients were categorized based on the value of %DLCO/VA. We assessed the impact of low %DLCO/VA on long-term prognosis and analyzed cause of death using propensity score matching.</p> Results <p>Sixty-seven (10.4%) patients died after achieving 5-year postoperative RFS, and the 5–10-year overall survival (OS) rate was 85.0%. After propensity score matching, there are 186 patients in the normal %DLCO/VA group and 93 patients in the low %DLCO/VA group. The 5–10year OS rate was significantly better in normal %DLCO/VA group than low %DLCO/VA group (81.5% vs. 64.0%; HR: 1.86). Moreover, among causes of 5–10year death, pneumonia-related deaths were significantly more frequent in the low %DLCO/VA group after propensity score matching (<i>p</i> = 0.04).</p> Conclusions <p>Our findings suggest that low %DLCO/VA value is a significant factor in long-term prognosis even after achieving 5-year postoperative RFS, and significantly increases the incidence of pneumonia-related deaths. Postoperative management to prevent pneumonia is essential for long-term survival of patients with low %DLCO/VA value.</p>