The recurrent episodes of hypoxia-reoxygenation (H/R) appear to be partly responsible for the increased oxidative stress in obstructive sleep apnea syndrome (OSAS). Peroxynitrite (ONOO-) is a product of the reaction of superoxide radical (O-2(-)) and nitric oxide (NO) and affects mitochondrial function and leads to cell death through oxidation and nitration reactions. The attacks of ONOO- on the proteins result in the nitration of tyrosine and lead to the formation of 3-nitrotyrosine (3-NT). The purpose of this study was to investigate the levels of total NO and 3-NT in OSAS. 3-NT was detected by competitive Elisa method and total NO was detected by modified Griess method in serum samples of patients with OSAS (n = 109) and healthy controls (n = 24). Compared to healthy controls, there was slightly increase in 3-nitrotyrosine levels and decreases in total NO levels in patients (p > 0.05). We observed effects of age, gender, and smoking on total NO. In OSAS group, statistically significant correlations were observed between 3-NT and triglyceride values in positive manner (r = 0.435, p = 0.0001) and between 3-NT and HDL levels in negative manner (r = 0,238, p = 0.033). Considering that proteins are much more resistant to oxidative damage than other biomolecules, even slightly elevated 3-NT values due to oxidative stress in patients with OSAS could be indicator of protein damage.