The aim of the present study was to determine changes in oxidative status in plasma of sows during periparturient period using markers of lipid and protein peroxidation intensity. Plasma from 12 pregnant gilts collected on days 14 and 1 before parturition and on days 1, 7 and 14 postpartum was used in the study. As indicators of alterations in the oxidative status, plasma concentrations of thiobarbituric acid reactive substances (TBARS) and sulphydryl groups (SH groups) were measured spectrophotometrically, as well as plasma concentrations of bityrosine and formylokinurenine were determined by the spectrofluorimetric method. Compared to the 14th day antepartum, the concentration of TBARS increased significantly on day 1 postpartum and then decreased significantly on days 7 and 14 after parturition. The concentration of SH groups increased significantly on the last day before parturition and decreased significantly on day 14 postpartum. The concentration of bityrosine increased significantly on the last day before parturition and decreased significantly on days 7 and 14 postpartum. The concentration of formylokinurenine increased significantly on the last day before parturition, remained at this level on the first day after parturition and then decreased slightly on days 7 and 14 postpartum. These results indicate that during periparturient period in sows, especially around the parturition, the oxidative/antioxidative balance is disturbed, which leads to oxidative stress. Considering that oxidative stress is potentially harmful for mothers and neonates, this may be an important factor in the increased risk of diseases occurring during this period.