From previous reports indicate that broiler chickens fed diets enriched with polyunsaturated fatty acids have less abdominal fat or total body fat (Sanz et al., 1999) deposition than do broiler chickens fed diets containing saturated fatty acids. In general, body fat accumulation may be considered the net result of the balance among dietary absorbed fat, endogenous fat synthesis (lipogenesis) and fat catabolism via β-oxidation (lypolysis). Thus, if the amount of absorbed fat is the same, lower body fat deposition may be attributed to increased fat catabolism or diminished endogenous fatty acid synthesis or to both process. Differences in lipid oxidation rates seem to be the main mechanism involved in this effect. Supplementation of unsaturated fatty acids in diets can be enhanced fat catabolism and reduced fatty acid synthesis were reported to occur in rats fed polyunsaturated fatty acid rich in diets compared with rats fed diets enriched with saturated fatty acids (Crespo and Esteve-Garcia, 2002). Polyunsaturated fatty acids rich in diet effect on fat absorption were increased. In, contrast amount of abdominal fat deposition was decreased. It may be that the polyunsaturated fatty acid was higher rate fat oxidation or lower rate of fatty acid synthesis or both. The present study was undertaken to determine the effect of amount of beef tallow versus soybean oil absorbed is the same on energy intake, energy excretion, energy retention and energy expenditure of broiler chickens.