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To evaluate in possible use of phytases for improving the utilization of low protein and energy diets, 420, one-day-old chicks were distributed among 7 groups (5 replicates of 12 chicks/group). During the starter (1–35 day), grower (37–56 day), and finisher (57–64 day) periods, the control group fed diets containing 21.2% crude protein (CP)-2947 Kcal/kg metabolizable energy (ME), 19.6 CP-3023 ME and 18.0 CP-3100 ME, respectively. The three low-CP groups received diets isocaloric but with −1% CP than the control, while the three low-CPME groups fed diets with −1% CP and −100 Kcal than the control. In addition, the low-CP and low-CPME groups were supplemented with 0 (low-CP_uns and low-CPME_uns), 500 U/kg of an Aspergillus niger (low-CP_AP and low-CPME_AP) or 500 FTU/kg of an Escherichia coli phytase (low-CP_EP and low-CPME_EP), respectively. Low-CP and low-CPME diets decreased (p &lt, 0.01) the intake of feed as well as the protein and metabolizable energy conversion ratios in comparison to the control group. In general, phytases lowered (p &lt, 0.01) the intake of feed, protein, and energy, but bacterial phytase showed a higher (p &lt, 0.01) effect than A. niger one. The diets with low-CP and low-CPME levels decreased (p &lt, 0.01) the amount of the excreta nitrogen. The supplementation of phytases had similar effects on digestibility of nutrients, carcass traits, bone mineralization and blood biochemistry. The supplementation of A. niger increased abdominal fat deposition of compared low-CPME diet compared to low-CPME_uns diet. All diets showed similar production index allowing the use of low-CPME diet when phytases was supplemented.