Objective: There is a crucial balance between oxidant and antioxidant defense mechanisms. We aimed to evaluate the role of the balance of these systems in community-acquired pneumonia (CAP) in children. Methods: We analyzed serum oxidant and antioxidant stress parameters according to the clinical and demographic data of children with CAP and compared them with healthy controls. Serum total antioxidant status (TAS), total oxidant status (TOS), and levels of ischemia-modified albumin (IMA), antioxidant enzymes, non-enzymatic antioxidant factors, and plasma thiol were evaluated and compared between the groups. Results: Of 160 children evaluated, 106 had CAP (54 outpatients, 52 inpatients) and the other 54 were healthy subjects (control group). Total thiol and native thiol levels were significantly lower in the inpatient group compared to the outpatient group (p=0.004, p=0.005). Serum IMA differed significantly among the groups (p=0.001), with inpatients showing the highest level. A positive correlation was found between serum IMA and C-reactive protein levels in patients with pneumonia (r=0.351; p=0.001). Conclusion: Parameters that provide information about antioxidant capacity may be useful in the diagnosis and prognosis of pneumonia. Both thiol homeostasis parameters and IMA level seem likely to be influenced by disease severity. Our results suggest that plasma thiol levels and IMA may be good candidate biomarkers to predict the severity of pneumonia in children.