In order to determinate the optimum level of energy and protein in broiler chicks fed diet containing cimaterol (CL 263, 780). an experiment which involved 3 levels of dietary energy (3500, 3200, 2900 ㎉ ME/㎏) and 2 levels of dietary protein (starter: 23, 20%: finisher: 20, 17%) was conducted. An in vitro trial was also carried out to study the activity of lipogenesis, lipolysis. protein synthesis and amino acid uptake. According to the results of 6 week feeding trial weight gains of the groups of 23-20%-3200 ㎉ and 23-20%-2900 ㎉ were significantly (p $lt;0.05) higher than that of 20-17%-3200 ㎉ group. At the same energy levels, growth rate tended to increase as the levels of protein increased (p$lt; 0.05). Among the energy levels. the growth rate at the medium level of energy was highest and feed efficiency was best. Feed intake decreased as the level of energy increased. The main factor determining the amount of fat deposited was the protein content of the diet in relation to the total energy. Abdominal fat quantity was increased as the energy-protein ratios widened (p$lt;0.05). At each protein levels, the higher energy group produced the more abdominal fat (p$lt;0.05). Carcass yields were not affected significantly by the plane of nutrition (p$gt;0.05), The size of giblets at the low protein groups (20-17%) were significantly (p$lt;0.05) greater than those of the high protein groups (23-20%). The results of in vitro trial showed that lipogenic activity tended to increase with increased energy level. The decreased energy level obtained the increased lipolytic activity. Dietary protein level did not show the consistent effect on the lipogenie and lipolytic activity. The high protein grous (23-20%) showed significantly lower ability of protein synthesis and amino acid uptake a than the low protein groups (20-17%). According to the above results. it was inferred that the addition of 0.25 ㎎ cimaterol to a ㎏ of finishing broiler diet did not affect conventionally accepted requirements for energy and protein. And it was also considered that a diet containing 23% protein and 3200 ㎉ ME,/㎏ for starter, 20% protein and 3200 ㎉ ME/㎏ for finisher would be suitable for optimum levels when 0.25 ㎎ cimaterol per ㎏ of feed was added.