The objective of the current study was to evaluate the effect of using different energy sources on performance and some carcass characteristics in Cobb 500 broiler chicks. A total of 600 one day-old Cobb 500 broiler chick with an average weight of 39 ± 0.50 g was randomly allocated into five treatments. Further each treatment was divided into four replicates. The chicks were fed a basal diet based on corn and energy level by Cobb 500 instruction manual as a control group, basal diet with 3% lesser energy than the control (E1), basal diet with 6% lesser energy than the control (E2), basal diet based on corn and fat level according to Cobb 500 instruction manual (E3), basal diet based on corn and fat with 3% upper energy (E4) for 42 days. The result of this study showed that there were significant differences between treatments compared to the control group. The feed conversion ratio of broiler chicks significantly increased (P≤0.01) by feeding E1, E2, E3 and E4. It was observed that the performance parameters showed little but significant differences (P≤0.01) throughout the experimental period. The result of this study showed that carcass, breast, liver, spleen and gizzard percentage increased by using treatments compared to the control. We concluded that the current nutritional recommendations in Cobb 500 broiler chicks' instruction manual are not sufficient to achieve the best growth performance of Cobb 500 broiler chicks.