Objectives <p>Loneliness is increasingly recognized as a determinant of poor prognosis in older adults with chronic diseases, yet its impact on community-acquired pneumonia (CAP) remains unclear. This study investigates the association between loneliness and long-term adverse outcomes in older CAP patients.</p> Methods <p>This is a multi-center, prospective cohort study. Patients aged ≥ 65 years with CAP were included from April 2021 to January 2023. At admission, self-reported loneliness, geriatric assessments, CAP severity, and laboratory parameters were evaluated. Participants were followed for 180 days post-discharge. The primary outcome was 180-day all-cause mortality; the secondary outcome was readmission for respiratory infection. Multi-variable Cox regression models assessed associations between loneliness and outcomes.</p> Results <p>A total of 619 older patients were included in the analysis, with a median age of 78 years, and 12.8% reporting loneliness. During the 180-days follow-up, all-cause mortality and respiratory infection-related readmission rates were 8.7% and 10.5%, respectively. After adjusting for confounders, lonely patients had a nearly twofold higher risk of 180-days post-discharge mortality compared to non-lonely group (adjusted HR:2.047; 95% CI:1.036–4.044) and no significant association was observed with hospital readmission.</p> Conclusions <p>Loneliness is an independent risk factor for all-cause mortality in the older patients with CAP. The assessment of loneliness and the implementation of targeted interventions may improve the long-term outcomes.</p> Registry <p>ClinicalTrials.gov</p> Registration date <p>19 April 2021</p> ClinicalTrials.gov ID <p>ChiCTR2100045574</p>