Protein is one of the most expensive portion of a broiler chicken diet. Overfeeding of protein may reduce broiler production profit as well as polluting soil through extra nitrogen excretion. Many attempts have been made to reduce dietary crude protein (CP) level with no adverse effect on broiler performance, as a result protein per se is no longer a requirement for growing chicken. Controversial results have been published with regard to lowering dietary CP level. The purpose of these studies was to pinpoint out the lowest possible dietary protein level when supplemental indispensable amino acids are maintained in a practical corn-soy diet.