This experiment was conducted to determine the effects of increasing energy level (higher than NRC, 1994 recommendation) using different fat levels and relative decreasing of protein and nutrient contents in the diet on blood biochemical parameters. With addition of three types of fats including tallow fat, soybean oil and poultry oil in two levels (4 and 8%) to basal diet that were already balanced on National Research Council (NRC, 1994) recommendations, seven different non-isonitrogenic and non-isocaloric diets were provided and given ad libitum. At 35 and 49 days of ages, blood samples were collected from wing vein and then by using Autoanalyser (ALCYON 300) sera were analyzed. Serum lipids concentrations including total cholesterol, triglycerides, HDL, LDL, VLDL and atherosclerosis indicators including LDL/HDL and T-CHOL/HDL showed no significant difference between dietary treatment groups. Serum LDL concentration and LDL/HDL indicator showed significant elevation from 35 to 49 d (p<0.01), whereas serum Cholesterol concentration showed decline at the same times (p<0.05). With increasing in dietary fat level from 4 to 8%, serum Cholesterol level showed significant elevation (p<0.05). Broiler chickens, probably because of bearing some physiological resistance systems, like over compensation (down regulation of lipoprotein lipase) are more resistant to high dietary fat intake.