The effects of different energy and protein levels on the growth performance, body protein and body fat of broilers aged from 1 to 21 days were investigated to identify the relationship between the efficiency of protein utilization for body protein deposition (ep) and energy∶protein ratio and the efficiency of energy utilization for protein and fat deposition. Four hundred and thirty-two one-day-old Arbor Acres (AA) broilers were randomly arranged into 24 treatments with 3 replicates in each treatment and 6 chicks in each replicate by sex and diets. Broilers were fed with 95%, 80%, 65% and 50% restriction of ad libitum intake, respectively. On each day, broilers were supplied with three allowances of high-protein basal diets and appropriate amount of starch which were determined by 4 feeding levels. Thus, 12 diets with different energy∶protein ratios were formed. The trial lasted for 21 days. At the beginning and the end of the trials, broilers were killed, and the body compositions were determined. The results showed as follows: 1) the different energy and protein levels significantly affected the final body weight, body protein and body fat weight of male and female broilers (P<0.05); at high level of protein, the final body weight, body protein and body fat weight of male and female broilers were significantly increased with the increase of energy intake (P<0.05); at middle level of protein, the body fat weight of male and female was significantly increased with the increase of energy intake (P<0.05), and at 50%～80% feed restriction, the final body weight and body protein weight of male and female broilers were significantly increased with the increase of energy intake (P<0.05); at low level of protein, the body fat weight of male broilers was significantly increased with the increase of energy intake (P<0.05), and at 50%～80% feed restriction, the final body weight and body fat weight of male and female broilers and body fat weight of female broilers were significantly increased with the increase of energy intake (P<0.05), but there was no significant difference in body protein weight of broilers (P>0.05); 2) the different energy and protein levels significantly affected the average daily gain of body weight, body protein and body fat (P<0.05), and the effects were the same to those of energy and protein intake on the final body weight, body protein and body fat weight of broilers; 3) with the increase of energy∶protein ratio, ep increased linearly at first, and then kept constant at last; when the energy∶protein ratio reached 69.28 MJ/kg, the ep of male and female broilers attained their maximum values, and was 0.64 and 0.63 respectively; 4) the efficiency of energy utilization for protein deposition in male and female broilers was 0.72 and 0.68, respectively, and the efficiency of energy utilization for fat deposition in male and female broilers was 0.59 and 0.65, respectively; male and female broilers needed 32.88, 34.82 kJ of ME per gram of fat deposition and 66.43, 60.12 kJ of ME per gram of protein deposition, respectively. The results above indicated that the levels of protein and energy affected the growth performance, body protein and fat deposition, the energy∶protein ratio affected the efficiency of protein utilization for body protein deposition; at the same time, some parameters required for broilers growth prediction model based on mechanism research were identified.［Chinese Journal of Animal Nutrition, 2010，22（4）:886-893］