This study was done to evaluate the effect of dietary supplementation of lemon grass and cinnamon powder on growth performance and carcass traits of Cobb500 broilers. A total of 360 Cobb500 broiler chicks at 14 days old was completely randomized design into 4 dietary treatments and three replicates with 30 chicks per each. The experimental diets were as followed as: control fed a basic diet without any herbal supplementation; S10 fed the basal diet plus 10g LGP/kg of feed; S10Q150 and S10Q250 fed the basal diet plus 10g LGP plus 150 or 250mg CP/kg of feed. Results showed that S10Q150 tendency reduced the infectious coccidiosis disease of broiler chicks compared to control and others. Moreover, S10Q150 was significantly highest BW and ADG whereas lowest values were on control. Slaughtered weight, carcass weight, dressing percentage, breast and thigh weights, breast and thigh meat weight as well as drip loss of breast meat recorded at 36 and 48h after slaughtered of dietary supplementations were improved significantly compared to control. It is possible suggested that supplementation of 1% LGP plus together with 0.015 or 0.025% CP to improve the growth performance and carcass traits of broiler chickens.