An experiment was conducted to study the effect of using different levels of protein (high, HCP; medium, MCP and low, LCP) along with different levels of phytase (0.0, 500, 750 and 1000 FTUlkg diet) in broiler diets on their growth performance, nutrients digestibility and economic efficiency. A total number of 360 one day old Arbor Acers broiler chicks were randomly divided into 12 groups (30 chicks each) of three replicates eacn (10 chicksireplicate). Twelve experimental diets were formulated in a 3 x 4 factorial design (Le. three levels of protein; HCP, MCP & LCP each was assigned to four levels of phytase; 0.0, 500, 750 and 1000 FTUikg)- The experimental birds were reared under similar managerial and veterinarial conditions and fed the experimental diets up to 7 weeks of age. At Y weeks of age, a digestion trials were carried out to study the effect of treatment on nutrients digestibility, energy metabolizability, nitrogen balance and minerals retention. The obtained data revealed that the chicks fed HCP diets recorded significantly the best growth performance including live body weight (LBW), body weight gain (BWG), feed intake (Fl), feed conversion (FC) and performance index (Pl) compared to the other levels (MCP and LCP), while did not affect CP digestibility, energy metabolizability and nitrogen balance (NB), but lowered crude fiber (CF), nitrogen free extract (NFE) and organic matter (OM) digestibility, and improved EE digestibility. Supplementing diets with phytase at levels up to 1000 FTUikg improved all growth performance parameters, with the level of ?50 FTUikg diet being the best compared to control (the unsupplemented diet). The addition of phytase did not affect nutrients digestibility except CF digestibility which improved by adding 750 FTUikg diet. Concerning the interaction effect, the obtained data revealed that the group of chicks fed HCP + 500 FTUIkg recorded significantly the heaviest LBW and BWG and consumed higher amount of feed allover the experimental period (0 -— ? wks), while the group of LCP + zero enzyme recorded significantly the lowest values of LBW, BWG, Fl, FC and Pi, as compared to the control. The gl'OUp of chicks fed HCP + 1000 FTUikg diet revealed significantly the best values of FC and PI as well as better values of CP, EE and OM digestibility, energy metabolizability and NB compared to the control, while those having LCP diet without phytase supplementation exhibited worst values of FC and Pi. However, the group of chicks fed MCP diet + 750 FTUikg recorded the highest CF digestibility. Meanwhile, the grow of chicks fed LCP diet + 750 FTUikg recorded the lowest feed cost needed to obtain one kilogram of awe. It could be concluded that supplementing MCP broiler diets with microbial phytase at 750 FTUikg improved their growth performance and nutrients digestibility being similar to the control, however, supplementing LCP diet with 750 FTUlkg resulted in the least feed costfkg gain.