The present study was conducted to investigate the effect of dietary emulsifier supplementation on performance, blood biochemical parameters, immune responses and ileal nutrient digestibility in broiler chicks fed on different metabolizable energy levels. A total of 432 one-day old Ross 308 broiler chicks were randomly distributed between 9 experimental treatments with 4 replicates. Each cage included 12 birds. Dietary treatments consisted of a 3×3 factorial arrangement with three dietary ME levels (control, 75 and 150 kcal/kg below control) and three levels of an emulsifier supplement (0, 0.05 and 0.1 % of diet). The experiment lasted 42 d, and chicks had free access to feed and water throughout the trial period. Performance parameters including average daily gain (ADG), average daily feed intake (ADFI) and feed conversion ratio (FCR) were measured periodically as 1-14 (starter), 15-28 (grower) and 29-42 (finisher) d of age. Serum samples were taken after immunization against Newcastle disease virus (NDV), infectious bronchitis virus (IBV) and infectious bursal disease virus (IBDV, Gumboro) to measure antibody responses against mentioned antigens. In addition, two birds from each replicate were injected intraperitoneally with 0.5 cc 5% suspension of sheep red blood cells (SRBC) at d 27 and 34, and serum samples were collected at 7 th d after each antigen inoculation to evaluate primary and secondary antibody responses to SRBC. At 42 d of age, two randomly-selected birds per each replicate were slaughtered and relative weights of internal organs and carcass characteristics were measured. The birds were fed marker-containing diets during the last 3d of trial and after euthanasia, the ilealdigesta were collected for investigation of ileal nutrient digestibility. Results showed that decrease in dietary ME level causes significant reduction in body weight gain during all periods. Dietary supplementation of emulsifier caused marked (P 0.05) growthin body weight gains during grower and finisher period. There was a significant (P 0.05) interaction between ME level and emulsifier supplementation in the grower and total period for ADG. The different levels of ME had no considerable impact on ADFI. The emulsifier supplement significantly (P 0.05) increased ADFI in finisher and total period. FCR significantly increased in total production period as a result of reduced dietary metabolizable energy. Furthermore, the emulsifier addetives could improve FCR in starter (P 0.05), grower (P 0.001) and total (P 0.05) periods. In addition, this improvement was more in chickens that received 0.1% emulsifier. The relative weight of internal organs such as the liver, heart and pancreas was not affected by different levels of metabolizable energy. But the relative weight of abdominal fat was significantly (P 0.05) impressed. So that, the relative weight of abdominal fat with minimal energy levels were dramatically decreased. A significant interaction effect (P 0.05) between the emulsifier and the level of ME on the relative weight of abdominal fat were observed. The different levels of energy, as well as complementary emulsifier, had no effect on the weight of the lymph organs. Low-energy diets decreased antibody titers against SRBC at first timing. Antibody titers against Gumboro at treatment 75 kcal below control, significantly higher than other groups. But LPC did not affect any antibody titers. A noteworthy interaction between ME level and emulsifier additives (P 0.05) in primary and secondary antibody response against SRBC was observed. As expected, reduction of dietary energy level reduced significantly (P 0.05) serum triglyceride level in chickens. However, HDL and LDL concentrations were unaffected. LPC greatly increased (P 0.001) serum triglycerides in birds. Energy level and emulsifier had no significant effect on levels of aspartate-amino transferase (AST) and alanine-amino transferase (ALT) enzymes. By reducing the level of dietary energy, T 3 hormone concentration linearly decreased. However, with the increase of LPC level, the concentration of T 3 and subsequently T 3 /T 4 ratio were dramatically (P 0.05) increased. By reducing the level of dietary energy, CP digestibility significantly (P 0.05) increased. Supplementation of emulsifier to the diet resulted in a significant increase (P 0.05) digestibility of EE. This, as well as improve the digestion and absorption of lipids by emulsifying and gives confirmation. Also the organic matter digestibility by adding an emulsifier to the diet (P 0.05) increased. The results of this study suggest that the use of complementary emulsifier can increase broilers performance, particularly by improving the digestibility of lipids.