We studied the influence of different selenium (Se) levels on some parameters of the antioxidant potential of lactating sows. The experiment involved 15 sows of the Large White breed divided into 3 equal groups. The addition of Se (from Se-enriched yeast) amounted to 0.0, 0.25 and 0.50 mg per kg of diet in the control, Se1 and Se2 groups, respectively. Erythrocyte Se concentration, glutathione peroxidase (GPx) activity and reduced/oxygenated glutathione ratio were measured as some of the indicators of the sow’s antioxidant status. Supplementation of Se at 0.25 mg/kg of diet increased Se concentration (by 50.0%; P<0.01), GPx activity (by 17.0%: P<0.05) and reduced/ oxygenated glutathione ratio (by 29.7%; P<0.05). Addition of Se at 0.50 mg/kg of diet increased Se concentration (by 63.6%; P<0.01), GPx activity (by 34.7%; P<0.01) and reduced/oxygenated glutathione ratio (by 64.0%; P<0.01). A significant relationship (P<0.01) was found between the Se concentrations and activity of GPx in erythrocytes from sows in the Se1 and Se2 groups (r=0.76 and 0.77, respectively). Percentage of piglets weaned/born was higher (P>0.05) in the Se2 than in the Se1 and control groups. In summary, addition of 0.25 or 0.50 mg Se/kg of diet can improve antioxidant status of lactating sows, but addition of 0.25 mg Se/kg may be also sufficient.