The current study was conducted to evaluate the efficacy of Thymbra spicata and Echinacea purpurea powders as alternatives to antibiotics in broiler chickens. A total of 192 one-d-old broiler chicks (Ross 308) were randomly allotted to 6 dietary treatments in a completely randomized design with 4 replicates of 8 birds. The experimental diets were as follows: 1) basal diet without additive (control group); 2) basal diet supplemented with Erythromycin (55 ppm); 3) basal diet supplemented with Thymbra spicata powder (2.5 g/kg ration; TSP-1); 4) basal diet supplemented with Thymbra spicata powder (5.0 g/kg ration; TSP-2); 5) basal diet supplemented with Echinacea purpurea powder (2.5 g/kg ration; EPP-1) and 6) basal diet supplemented with Echinacea purpurea powder (5.0 g/kg ration; EPP-2). All of the birds had free access to water and feed throughout the trial and were oral gavaged with Campylobacter jejuni (4 × 1011 cfu/mL) on d 21. During the finisher period, FCR was improved in broiler chicken fed the EPP-1, EPP-2, TSP-1 and Erythromycin, and supplementation of diets with EPP-2 and TSP-1 led to an increased European production efficiency factor when compared with control group (P < 0.05). In addition, feeding broiler chickens with EPP-1, EPP-2, and TSP-1 caused to an improvement in FCR during the entire period (P < 0.05). Gastrointestinal microbial population was not affected by supplementation of diets before inoculation (P > 0.05). However, the addition of EPP-1, TSP-1, and TSP-2 in broiler diets caused to an increase in enumeration of Bifidobacteria and a decrease in colonization of Campylobacter jejuni at 3 week post-inoculation (P < 0.05). In addition, villous length and villous surface area in the duodenum was increased in broiler chickens fed the TSP-1 diet, when compared with those fed the NC diet (P < 0.05). In addition, feeding broiler chickens with the EPP-1 resulted in an increase in the villous length of the ileum (P < 0.05). However, there were no diffe