Abstract: A 42 d broiler experiment was conducted to determine the effect of added Escherichia coli phytase (Phyzyme-XP 5000G) to low and high phytate P (PP) diets on performance and nutrient digestibility. The experiment consisted of 12 treatments with 2 levels of PP: Low-Phytate (LP) group-0.24% and High-Phytate (HP) group-0.32%. Both LP and HP groups had respective Positive Controls (PCs) with 0.39% in the starter and 0.29% NPP in the grower, respectively and 5 basal diets with graded levels (0, 250, 500, 750 and 1000 FTU’s/kg diet) of added phytase. The HP diets contained additional PP because canola and rice bran were substituted for part of the corn and soybean meal. A significant (p<0.001) phytase effect was found for Body Weight Gain (BWG) Feed Intake (FI) and Feed:Gain (F:G) ratio on d 42 and ileal P digestibility and % tibia ash for both LP and HP groups on d 42. Supplementation of 250 FTU’s phytase/kg diet for both LP and HP basal diets produced equivalent body weights (p>0.05) to comparable respective PCs. Supplementing 500 FTU’s phytase/kg diet in both LP and HP groups resulted in a comparable (p>0.05) % tibia ash to respective PC groups. The litter Total Dissolved P (TDP) and Water-Soluble P (WSP) of pens from broilers fed either the LP or HP basal diets with increasing concentrations of phytase were not significantly different (p>0.05) compared to the respective PCs. The research shows that adding feed phytase does not necessarily mean that TDP and WSP will be reduced. The P equivalency determined from 42d ileal digesta for added phtase with the LP and HP diets showed that broilers fed the HP diet with 1000 FTU phytase provided 0.17% digestible P compared to 0.13% digestible P from the LP diet. In order to decrease P excretion in broilers, added feed phytase should be considered equal to feed phosphates for providing available P in the gastrointestinal tract and the combination needs to be low enough for optimum performance and retention.