two experiments were carried out to determine the ideal levels of crude protein (cp) for ross broiler chickens from one to 21 and 22 to 42 days of age, of both sexes. the parameters evaluated were weight gain (wg), feed intake (fi), feed:gain ratio (f/g) and carcass evaluation (cv). in the starting phase (1 to 21 days of age), different protein levels (20.00; 20.50; 21.00; 21.50; 22.00 and 22.50%) were used in diets containing 1.27% total lysine. in growing phase (22 to 42 days of age), the dietary protein levels were 17.50; 18.00; 18.50; 19.00 and 19.50% with 1.16% total lysine. in both experiments, were maintained ratio lysine: methionine+cystine, threonine, tryptophan and arginine, considering the ideal protein profile. in both experiments, a completely randomized block experimental design, in a 2x6 and 2x5 (two sexes and six or five dietary lysine levels) factorial arrangement, was used, with six replicates, using a total of 1440 and 1200 birds, respectively. considering bird performance, the dietary cp requirement estimate from 1 to 21 days, for the males was 22.42% cp, while the females showed linear effect for wg and f/g. in the growing phase (22 to 42 days of age), the protein levels affected linearly males fi, f/g, breast yield and abdominal fat. females showed quadratic effect for wg and linear effect for f/g and abdominal fat. the requirements of the crude protein estimates for male and female, respectively were: 22.4 and 22.5% cp for starting phase and 19.5 and 18.5% cp growing phase.