Objectives: The aim of the present study was to evaluate the effect of different levels of dietary metabolizable energy and copper-methionine supplement on internal organ weights of broilers. The major portion of poultry feed is used for energy production to provide the maintenance and growth requirements. The increasing of dietary metabolizable energy decreases feed consumption and improves body weight gain and feed conversion ratio of broilers. The raising of dietary metabolizable energy is mainly done via addition of oils and fats. The dietary oil and fat sources may be oxidized and need to the presence of antioxidants for prevention of oxidation. Peroxidation of liver fats may disturb antioxidant defense mechanisms of hens, cause oxidative damage and make the liver prone to bleeding. Copper is a part of superoxide dismutase enzyme. Superoxide dismutase neutralizes free radicals. Therefore copper has antioxidant property and can protect internal organs such as heart, liver and pancreas from oxidative damage. Materials & Methods: A total of 576 one-day old Ross 308 male broiler chicks were allotted in a 3×4 factorial arrangement with completely randomized design to 12 treatments and 4 replicates of 12 chicks in each. The factors of interest included different levels of dietary metabolizable energy (at Ross catalogue recommendation (3025 kcal/kg), 100 kcal lower than that of Ross catalogue recommendation (2925 kcal/kg) and 100 kcal higher than that of Ross catalogue recommendation (3125 kcal/kg)) and different levels of dietary copper-methionine supplement (0, 150, 300 and 450 mg/kg). The diets were formulated according to Ross 308 catalogue recommendations. The lighting program included 23 hours lightness and 1 hour darkness. Feed and water were provided ad libitum throughout the experimental period. At 49 day of age, one bird with body weight nearest to average body weight of the experimental unit was selected and slaughtered after weighing and internal organ wei
