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To enrich pork with valuable n-3 PUFA, it is common practice to include flaxseeds in the swine diet. However, due to the high susceptibility of these acids to oxidation, this treatment requires an additional supply of antioxidants. Thyme herb can be used for this purpose, which in addition to high antioxidant activity is characterized by numerous health-promoting properties. The present study aimed at evaluating the impact of the inclusion of 1% and 3% of thyme herb in mixtures with 4% of extruded flaxseeds as a source of n-3 PUFA on the performance results and health status of fatteners. The experiment was carried out on 120 weaners with an initial body weight of about 30 kg and kept until the end of fattening. They were divided into three experimental groups of 40 animals each (5 pens with 8 pigs in each). The control group (C) consisted of pigs receiving a base mixture with 4% of extruded flaxseeds. In the experimental groups, an additional 1% (T1) or 3% (T3) of thyme herb was added to the mixture. By supplementing the diet with 3% of thyme, an increase in average daily weight gain (P = 0.001) and a better feed conversion ratio (P < 0.001) were obtained. This could be the result of an improvement in the small intestine histology (greater villus height–P < 0.001) and better digestibility of basic nutrients (especially crude protein–P < 0.05) found in experimental animals. In addition to these effects, thyme herb supplementation contributed to the stimulation of immune mechanisms (increase in the number of WBC–P ≤ 0.05; plasma IgA ‐ P < 0.05 and IgG–P < 0.005, and the level of lysozyme–P < 0.05). The obtained results indicate the advisability of the use of thyme as a feed additive beneficially influencing the health and performance results in pigs. The obtained results indicate the advisability of the use of thyme as a feed additive beneficially influencing the health and performance results in pigs.