The study determined the effect of addition of 2-3 % of garlic (AL2, Al.3) and its combination with 1 % of thyme (AL.2.Th, Al.3.Th) to iso-caloric and iso-nitrogenous diets for broiler chickens on the nutrient digestibility, production traits, slaughter analysis parameters, hematological and biochemical blood indices, and the weight of breast, drumstick meat, and chosen organs. Two hundred fifty one-day-old broiler chickens were assigned to five groups (treatments) with 5 replicates (10 birds per cage, 5 females and 5 males). The experiment lasted 6 weeks. Broiler chickens receiving diets supplemented with the herbs exhibited an increase (P = 0.025) in the average body weight (about 9,1 % vs C) and body weight grain (about 20,7 % vs C) in the finisher period and an increase (P < 0.05) in the organic matter digestibility of the diets (about average 6,9 % vs C). An improvement in the FCR (P = 0.019) index was noted in broiler chickens fed the herb-containing mixtures in each combination in the finishing period (even about 14,4 % vs C in Al.2.Th). Moreover, the best carcass quality with a high proportion of muscles and low abdominal fat content (P = 0.031) was noted in broilers feed 2 % of garlic + 1 % of thyme and 3 % of garlic + 1 % of thyme-enriched diets. The addition of the herbs into the diets contributed to an increase in the number of Lactobacillus and Enterococcus bacteria (P = 0.018) and a decrease in Escherichia coli counts in the small intestine, compared with the control treatment (respectively about 6,3 %↑ and 6,5 %↓ in Al2.Th and Al.3Th). No Salmonella sp. were isolated in any treatment. Additionally, an increase in the percentage of lymphocytes (about 17,1 %) and a simultaneous decrease in the granulocyte (about 17,9 %) count were observed in the blood of broiler chickens AL.3, AL2.Th and Al.3.Th treatments. In summary, incorporation of thyme and/or garlic into the diet for broiler chickens can effectively improve growth performance, carcass parameters, gut microbiota, and the defense potential in the organisms of broiler chickens.