The association between Atrial Fibrillation (AF) and pneumonia remains unclear. This study aims to assess the impact of AF on high pneumonia risk group—chronic obstructive pulmonary disease (COPD)—In order to find the association between AF and the risk of pneumonia. The COPD cohort was extracted from National Health Research Institute of Taiwan. The AF cohort comprised all COPD patients with new-onset AF (International Classification of Diseases (ICD)-9 code 427.31) after COPD diagnosis. We further sampled non-AF cohort and performed 1:1 propensity score matched analysis to improve the balance of baseline characteristics between AF and non-AF cohort. The outcomes were pneumonia and pneumonia requiring mechanical ventilation (MV). From 2000–2011, a total of 6228 patients with COPD and AF, and matched 84,106 control subjects were enrolled. After propensity score matching, we identified 6219 patients, each with AF, and matched controls without AF. After propensity score matching, the AF cohorts had higher risk of mortality (adjusted hazard ratio (aHR), 1.24; 95% confidence interval (CI), 1.15–1.34), pneumonia (aHR, 1.17; 95% CI, 1.07–1.27), and pneumonia requiring MV (aHR, 1.33; 95% CI, 1.18–1.50) in comparison with the matched non-AF cohort. After adjusting for mortality from causes other than outcomes of interest as a competing risk, AF remains significantly associated with pneumonia and pneumonia requiring MV. The risks of pneumonia were higher in this population with AF than in those without AF, and the risk was still significant after the adjustment for the competing risk of all-cause mortality. [Full article]