Plant-based diets are recommended for cancer survivors; however, their effects on lung cancer mortality are limited. We conducted this study to evaluate the association between plant-based dietary patterns and lung cancer mortality. A total of 408 newly diagnosed lung cancer patients aged 18 to 79 years were enrolled in the study. Dietary intake was assessed using a validated 111-item food frequency questionnaire (FFQ). The survival status was confirmed by medical records and an active follow-up until March 31, 2023. We calculated three dietary indices: the overall plant-based diet index (PDI), the healthful plant-based diet index (hPDI), and the unhealthful plant-based diet index (uPDI). Cox proportional hazards regression models were used to evaluate the hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of plant-based indices with lung cancer mortality. During the follow-up period (median: 40.97 months; interquartile: 29.77-45.63 months), 240 patients died from lung cancer. An inverse association was observed between hPDI scores and lung cancer mortality (Q4 vs. Q1, HR, 0.66, 95% CI, 0.45-0.97, the P value for trend, 0.042), while each 10-unit increment was associated with a decreased risk of lung cancer mortality (HR, 0.75; 95% CI, 0.57-0.99). Regarding PDI and uPDI, no significant association was found with lung cancer mortality. Our study suggests that adherence to a diet with a high hPDI score may reduce lung cancer mortality.