To evaluate effectiveness of 23-valent pneumococcal polysaccharide vaccine (PPSV23) inoculated during defined "vaccination period," first 6 months post cancer diagnosis (ie, an anti-cancer treatment period), in elderly lung cancer patients on community-acquired pneumonia (CAP) hospitalization incidence.This was a nationwide population-based cohort study of 157 newly diagnosed elderly lung cancer patients receiving PPSV23 during "vaccination period", and 628 age and sex one-to-one matched controls enrolled in the National Health Insurance Research Database (NHIRD) of Taiwan between 2007 and 2010. All patients were ≥75 years old and still survival post "vaccination period." Incidence density (ID) of all-cause inpatient CAP and cumulative survival risk were analyzed by multivariate Poisson regression and Kaplan-Meier method, respectively.After a 4-year follow-up, IDs of all-cause inpatient CAP for vaccination and control cohorts were 297 and 444 per 1000 PYs, respectively. Less vaccinated patients had CAP incidence density >1 time per PY (12.7% vs 21.2%) than non-vaccinated patients. After adjusting for potential confounding variables, like influenza vaccination, comorbidities, cancer treatment modalities, and socioeconomic status, adjusted inpatient CAP incidence rate in PPSV23 vaccination cohort was 0.74 times lower than control cohort (incidence rate ratio [IRR] = 0.740, P = 0.0339). Two-year cumulative CAP hospitalization rates and overall survival rates were 37.1% vs. 55.4%, and 46.6% vs. 26.2%, respectively, for lung cancer patients with and without PPSV23 (both P < 0.001). Subgroup analysis showed that for elderly lung cancer patients not ever receiving influenza vaccine, PPSV23 still had trend to reduce all-cause inpatient CAP.For elderly lung cancer patients aged ≥75 years, PPSV23 inoculated during anti-cancer treatment period could reduce CAP hospitalizations and improve survival.