The aim of the study was to investigate the effect of the feed additive “Butaselmevit-plus” on the state of the antioxidant defense system of piglets during weaning. The experiments were conducted on the basis of the LTD “KOSHET” Mukachevo district of Zakarpattia region. Two groups of piglets were formed – control and experimental, in the amount of 10 individuals in each group, selected on the principle of analogs – age, breed and body weight. Animals were fed according to the norms for this age of pigs. On the 28th day of life, the piglets were weaned from the sow and regrouped from different nests for further maintenance during fattening and rearing with a change in the structure of the diet, which served as technological stress for the animal's body. Piglets of the experimental group, from 21 to 40 days of age, were additionally fed the feed additive “Butaselmevit-plus” at a dose of 100 mg/kg body weight per day. The material for the study was blood, which was taken in the morning before feeding the animals by puncture of the cranial vena cava for 20 days of life (the period before weaning), for 25 days of life (the period before weaning), for 30 days of life (2 days after weaning), for 35 days of life (7 days after weaning), 40 days of life (12 days after weaning). It is proved that feeding piglets feed additive “Butaselmevit-plus” enhanced the antioxidant status of piglets after weaning. It was found that under conditions of technological stress, the use of feed additive “Butaselmevit-plus” in the amount of 100 mg/kg body weight per day improves the antioxidant defense of the body, as evidenced by an increase in blood 35-day-old piglets superoxide dismutase activity by 26.7 % (P < 0.001), catalase – by 39.5 % (P < 0.001), glutathione peroxidase – by 51.7 % (P < 0.05), glutathione reductase – by 52.9 % (P < 0.05), the content of reduced glutathione – at 58.3 % (P < 0.001). These results confirm the effectiveness of the use of milk thistle, methionine, selenium, and vitamins A, E, and D3 in the feed additive “Butaselmevit-plus” to piglets in the period before and after weaning to activate the protective systems of their body.