Summary Background. Lichen planus (LP) is an autoimmune inflammatory disease of the mucocutaneous tissue, whose exact pathological course is not yet understood. Many studies have implicated the role of reactive oxygen species (ROS) and the protective role of antioxidants in several autoimmune skin disorders. In this study, serum levels of antioxidants in patients with LP were determined and compared with those of healthy controls. Methods. In total, 30 patients with LP (mean ± SD age 41.63 ± 13.03), who had never received treatment for their disease, were enrolled; 30 healthy people (aged 41.17 ± 13.24) were recruited as the control group. Serum levels of glutathione peroxidase (GPX), vitamin C, selenium, bilirubin and uric acid were determined. Results. The mean plasma level of vitamin C was significantly lower (P < 0.001) in patients compared with controls. A significant positive correlation was found between selenium and GPX in both patients (Spearman ρ = 0.99, P < 0.001) and controls (ρ = 0.10, P < 0.001). Conclusions. Lower serum levels of vitamin C in patients with LP indicates that free radicals and the resulting oxidative damage may be important in the pathogenesis of LP lesions.