The study was conducted to examine the effects of a phytogenic feed additive (PFA; BIOSTRONG® 510) on growth performance, selected blood parameters and jejunal morphology in broiler chickens. The PFA consists of a mixture of essential oils with thymol and anethole as leading active substances, as well as different herbs and spices. A total of 264 1-d-old Cobb male broilers were randomly allocated to 2 dietary treatments, with 6 replicates per treatment and 22 birds each replicate. The experiment lasted 42 days. The dietary treatments were a starter and grower diet without feed additives (control), or the diets supplemented with 150 mg/kg of the PFA. Body weight and feed intake were not significantly influenced by PFA feeding compared with the control during all experimental periods. During the grower phase (22 -42 d of age) and during the whole period (1 -42 d of age) the PFA significantly improved (P<0.05) feed conversion ratio. Serum total protein, albumin, total cholesterol and leucocytes were increased by PFA feeding. Furthermore, villus height to crypt depth ratio in the jejunum was increased by PFA feeding. In conclusion, the results of this study show that inclusion of PFA lead to morphological changes in the jejunum, which might influence nutrient absorption and thus, improved FCR.