Background and objective: Oxidative stress has an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). There are studies suggesting a role of increased oxidative stress and decreased antioxidants in COPD patients. The aim of this study was to assess the levels of oxidative and anti-oxidant system elements, serum concentrations of trace elements, and blood viscosity in COPD patients. Materials and methods: Our study group consisted of 25 male patients with COPD, and 25 healthy non-smokers. The lipid peroxidation product malondialdehyde (MDA) and the anti-oxidant system elements superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) were measured spectrophotometrically. Serum concentrations of copper (Cu), zinc (Zn), and iron (Fe) were determined using an atomic absorption spectrophotometer. Additionally, we measured blood viscosity using a viscosimeter. Results: Lipid peroxidation product MDA levels were found to be higher in plasma and erythrocytes. However GSH levels, SOD, and CAT enzyme activities were lower in erythrocytes of the patient group than in controls (p < 0.01). Fe and Zn levels were decreased, whereas Cu levels were increased in patient samples (p < 0.05. p < 0.01, respectively). There was no statistically significant difference between plasma and blood viscosities. Conclusion: The results of this study indicate that COPD leads to lipid peroxidation in the erythrocyte membrane and to decreased levels of anti-oxidant system elements. Serum trace element concentrations were found to be altered in COPD patients, suggesting their interaction with oxidant and anti-oxidant enzymes.