This experiment was conducted to study the effect of using low crud protein level fortified by lysine and methionine with or without microbial phytase on growth, feed utilization, carcass characteristics, blood constituents and economic efficiency of broiler chicks. Corn – soy bean basal diet was formulated to 23 - 21 – 19 % CP and 3000 - 3100 – 3200 kcal ME / Kg diet, used during starter, grower and finisher experimental periods. While, the second group fed low crud protein 3% points (20 – 18- 16 % CP) and lysine (Lys) and methionine (Met) level containing diets 90% with 500 FTU phytase during experimental periods compared to control basal diet, whereas the third groups fed 2 diets without phytase respectively, the fourth and fifth groups received the same diet fortified by lysine and methionine 100% from the requirements of strain recommendation with or without phytase supplemented respectively. While, groups 6 and 7 fortified their diet by Lys and Met up to 110% from the requirements of strain recommendation with or without phytase supplemented respectively. A total of 315 unsexed day-old Ross × Ross 308 broiler chicks were randomly distributed into 7 groups of similar chick numbers. The criteria considered were live body weight (LBW), body weight gain (BWG), relative growth rate (RGR), feed consumption (FC) and conversion ratio (FCR), protein intake, metabolizable energy intake and utilization (MEU), lysine intake (Lys.I), methionine intake (Met.I), slaughter characteristics and blood constituents. The economic efficiency of the product was also calculated. The obtained data showed that reducing the protein concentration resulted in (LBW), (BWG), (RGR), (FC), (FCR), protein efficiency ratio (PER), protein conversion ratio (PCR), MEU), (Lys.I), (Met.I), Liver weight, relative weight of dressing and abdominal fat, serum total protein and albumin, net return (NR) and economic efficiency significantly increased by fortified Lys & Met with phytase supplementation than other groups. The results indicate that it is possible to reduce crude protein diets by 3% and fortified Lys & Met in starter, grower or finisher broiler chicken rations with adding phytase to these rations without negative effect on growth performance, feed utilization, carcass characteristics and blood constituents.