The aim of the current study was to evaluate the effects of supplementing sow diets with oregano essential oils (OEO) during gestation and lactation on oxidative stress status, lactation feed intake and reproductive performance of sows. Sixty multiparous large white sows were randomly assigned to 1 of 2 dietary treatments within 24h after service to weaning: control (C) or C+ 300mg/kg of OEO (OEO). Serum samples collected from sows on d 10, 60, 90 and 109 of gestation and d 1, 3, 7 and 21 of lactation were used to determine reactive oxygen species (ROS), glutathione peroxidase (GSH-Px) and oxidative stress markers [malondialdehyde (MDA), 8-hydroxy-deoxyguanosine (8-OHdG)] levels. Data were analyzed using GLM procedure. The average daily gain (ADG) of suckling piglets was subjected to analysis of covariance with the piglet weight after cross-foster as the covariate. Variations of oxidative stress parameters were using the procedure for repeated measurements, which included the effects of treatment, physiological stage and replicate. Differences between means were significant at P < 0.05 and trends identified when P > 0.05 but ≤ 0.10. The results showed that serum levels of ROS, MDA and 8-OHdG were higher (P < 0.05) during gestation (d 90, 109) and lactation (d 1, 3) than early gestation (d 10). Sows fed OEO diet elevated serum concentration of GSH-Px on d 60 of gestation (P = 0.08), and d 1 (P = 0.07) of lactation than C group, while serum concentrations of MDA on d 1 of lactation (P < 0.01), 8-OHdG on d 109 of gestation (P = 0.09), d 1 (P = 0.06) and d 3 (P = 0.10) of lactation and ROS on d 1 (P = 0.10) and d 3 (P = 0.10) of lactation were lower in sows treated with OEO dietary than C group. Dietary OEO treatment increased sow feed intake in the third week of lactation (6.46 vs 6.03 kg/d, P = 0.07), accordingly, had higher ADG (252.36 vs 233.61 kg/d, P < 0.01) of suckling piglets of entire lactation than C group. In conclusion, our results demonstrated that there was an increased systemic oxidative stress during late gestation and early lactation of sows. Nevertheless, OEO dietary supplementation attenuated oxidative stress in sows.