Objective: In this study, we aimed to investigate oxidative stress and antioxidant parameter levels in patients with carbon monoxide (CO) poisoning. Methods: The study was conducted prospectively between March 1, 2015 and April 30, 2016 in the pediatric emergency department. Eligible patients included children aged 0-18 years old with a diagnosis of CO poisoning. To determination of oxidative stress and antioxidant parameter levels, venous blood with heparinized and urine samples were drawn during the admission and after normobaric oxygen (NBO) and hyperbaric oxygen (HBO) treatment. Results: Forty-seven children with CO poisoning for study group and 29 patients as control group were included to the study. Sixteen patients treated with HBO. Basal plasma malondialdehyde levels were found to be significantly higher in the CO poisoning group when compared with the control group (p = 0.019). There is no significant difference in oxidative stress and antioxidant parameter levels except erythrocyte catalase enzyme levels in patients treated with NBO when comparing before and after NBO treatment (p > 0.05). Decreasing of basal erythrocyte catalase enzyme levels were found statistically significant after NBO treatment (p = 0.04). There was no significant difference in oxidative stress and antioxidant parameter levels in patients treated with HBO before and after therapy (p > 0.05). Conclusions: CO poisoning is associated with increased lipid peroxidation in children immediately after the poisoning. However, both treatment modalities including NBO or HBO do not have a significant effect on oxidative stress or antioxidant parameter levels.