Oxidative stress is considered to be one of the mechanisms responsible for gluten toxicity, but its role in celiac disease (CD) remains unclear. The aim of the study was to evaluate oxidative imbalance in the pathomechanism of CD by determining the concentrations of nitric oxide (NO) and selected antioxidant parameters. The study involved 197 adult patients: 53 patients with untreated active CD, 92 celiac patients on gluten‑free diet (GFD), and 52 controls. The serum levels of antioxidants (uric acid, bilirubin, ferritin, albumin), celiac antibodies, NO, glutathione peroxidase 3 (GPx3), and vitamin E were measured. A histopathological study of duodenal biopsy was performed. Celiac patients had higher uric acid concentrations than controls (P <0.001). NO levels were higher in patients with active CD than in controls (P <0.01) and were correlated with the degree of mucosal damage ( = 0.04; P = 0.01). Vitamin E levels were decreased in celiac patients (P <0.01), and GPx3 activity was reduced in patients with active CD compared with controls (P <0.001).