摘要Objective: To test the effect of supplementation of Thymus vulgaris L. (T. vulgaris) or Glycyrrhizaglabra (G. glabra) in corn-soybean meal diets as well as the inclusion of an exogenous enzyme i.e. Combo ? in barley-soybean meal diets together with mentioned medicinal plants in broiler diets. Methods: A total of 270 unsexed 1-day-old broiler chickens (Ross 308) was randomly assigned to 6 treatments with 3 replications of 15 birds in each. Diets were comprised of the control (T1), the inclusion of T. vulgaris, G. glabra, their mixture (equal amount), Combo ? supplementation (T2, T3, T4 and T5, respectively) in diets based on corn-soybean meal diets and enzyme supplementation plus equal amount of tested medicinal plants (T6) based on barley-soybean meal diets. Medicinal plants and enzyme were included in diets at level 0.5% and 0.2% of diets, respectively.Results:The highest feed intake was obtained by T1 at 1-21 d of age (P<0.05). All diets caused significant increases in weight gain and significant decreases in feed conversion ratio compared to control at this age (P<0.05). Significant reductions were acquired in feed intake by T3 and T6 at 22-42 d of age (P<0.05). All diets significantly decreased total number of aerobic bacteria, coliforms, Gram-negative bacteria and increased lactic acid bacteria compared to control (P<0.05). Conclusions: The results showed that basal diet has vital character to effectiveness of medicinal plants in broiler diets. Beneficial effects on intestinal microflora were brought by use of T. vulgaris L. and G. glabra in corn-based diets or in barley-based diets together with enzyme. Thus, this capability can support growth performance of broiler chickens at lower age.