Background: Community-acquired pneumonia is an important cause of mortality and morbidity in all age groups. Oxidant and antioxidant mechanisms play an important role in the pathogenesis and mortality of community-acquired pneumonia. Objectives: In this study, the role of thiol/disulfide homeostasis in the diagnosis and prognosis of community-acquired pneumonia was investigated. Methods: This was a prospective, controlled, observational study involving 73 community-acquired pneumonia patients and 68 healthy volunteers. Results: The native thiol and total thiol, which are thiol/disulfide homeostasis components, were significantly lower in the community-acquired pneumonia group. It was also found that the native thiol was lower in the high-risk community-acquired pneumonia group and that the native thiol and total thiol were associated with the Pneumonia Severity Index, CRB65 (confusion, respiratory rate, blood pressure, > 65 years old), and CURB65 (confusion, uremia, respiratory rate, blood pressure, > 65 years old) scores. The thiol compound levels were also associated with the C-reactive protein and procalcitonin levels. However, there was no significant difference between the survivors and non-survivors in terms of the thiol/disulfide homeostasis parameters. Conclusion: This study demonstrated the important role that oxidative stress plays in the pathogenesis of community-acquired pneumonia. The thiol/disulfide homeostasis biomarkers especially the native thiol and index-1 levels were significantly lower in patients with community-acquired pneumonia. Further studies are needed to investigate the diagnostic and prognostic value of thiol/disulfide homeostasis parameters in community-acquired pneumonia.