Abstract: Due to environmental and economic concerns there is a great interest in providing adequate Phosphorus (P) level to sustain performance of poultry while reducing P excretion with manure to the environment. The purpose of the present study was to determine the effect of dietary Total Phosphorus (TP) in birds sorted into 2 groups: Heavy (H) and Light (L) from three to seven weeks of age on performance, serum phosphorus (serum P) and intestinal phytase activity. From three to six weeks of age, diets contained 5.0, 5.5, 6.0 and 6.5 g TP kg-1. From six to seven weeks, birds received diets that contained 3.8, 5.5, 6.0 and 6.5 g TP kg-1. At six and seven weeks of age interactions were not detected and either dietary TP or weight group had a significant effect on performance. Serum P was affected by the amount of inorganic phosphorus in the diet. Phytase activity was dramatically affected by diet; birds that received 3.8 g TP kg-1 diet (no inorganic supplement) had the highest activity. The results obtained from this study indicate that it is possible to reduce P excretion with no adverse effect on the performance from three to seven weeks of age. In conclusion, dietary P could be reduced to 5.0-5.5 g kg-1 from 3 to 6 weeks and omitted from the withdrawal diets without adverse effects on live performance and this could decrease P intake and as a result P excretion.