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Introduction: Obstructive sleep apnea (OSA) is characterized by repeated upper airway obstruction and intermittent hypoxia, which results in generation of reactive oxygen species. The resultant oxidative stress has been postulated as a trigger for cardiovascular and metabolic consequences. We studied the serum levels of three oxidative stress biomarkers in patients with OSA. Materials and methods: Newly diagnosed, treatment-naïve adults with OSA were included as cases. Healthy, nonsmokers, with no history suggestive of OSA were included as controls. Serum superoxide dismutase (SOD), thiobarbituric acid reactive substances (TBARS), and 8-hydroxy guanosine (8-OHdG) levels were assessed using enzyme-linked immunosorbent assay method. Results: Sixty patients (20 each with mild, moderate, and severe OSA, respectively) and 20 controls were included in the study. Median (interquartile range) serum levels of SOD were 31.4 ng/mL (24.8–35.5) and 41.9 ng/mL (29.6–58.3) in controls and OSA patients, respectively (p = 0.004). Serum SOD levels showed a weak negative correlation with apnea−hypopnea index (AHI) (P = –0.295; p = 0.022) and supine AHI (P = –0.261; p = 0.044). Median levels of 8-OHdG were not different between cases and controls (35.4 ng/mL (29.0–67.0) and 45.9 ng/mL (36.4–58.7); p = 0.237). Serum TBARS levels were 18.6 ng/mL (14.8–30.6) and 51.06 ng/mL (15.93–84.11) among cases and controls, respectively (p = 0.005). Conclusion: Serum levels of SOD were significantly lower among patients with OSA compared with controls and showed a negative correlation with the severity of OSA. This may be indicative of a reduction in antioxidant reserve secondary to oxidative stress.