Background:The reduction of crude protein levels in diets for broiler chickens may generate economic,environmental and flock welfare and health benefits;however, performance is usually compromised. Whole grain feeding and phytase may improve the utilization of reduced crude protein diets. Results:The effects of pre-pellet cracked maize (0, 15％and 30％) and phytase (0, 750 and 1500 FTU/kg) in iso-energetic maize-soy diets with three levels of crude protein (22％, 19.5％and 17％) were evaluated via a Box-Behnken response surface design. Each of 13 dietary treatments were offered to 6 replicate cages (6 birds/cage) of male Ross 308 broiler chicks from 7 to 28 d post-hatch. Model prediction and response surface plots were generated from experimental data via polynomial regression in R and only significant coefficients were included and discussed in the predicted models. Weight gain, feed intake and FCR were all influenced by pre-pellet cracked maize, phytase and crude protein level, where crude protein level had the greatest influence. Consequently, the reduction from 22％to 17％dietary crude protein in non-supplemented diets reduced weight gain, feed intake, relative gizzard weight, relative gizzard content and relative pancreas weight but improved FCR. However, the inclusion of 30％cracked maize to 17％crude protein diets restored gizzard weight and 1500 FTU phytase inclusion to 17％crude protein diets increased relative gizzard contents and pancreas weights. Cracked maize and phytase inclusion in tandem to 17％crude protein diets increased weight gain, feed intake and FCR;however, this FCR was still more efficient than broilers offered the non-supplemented 22％crude protein diet. Broilers offered the pre-pellet cracked maize and phytase inclusions reduced AME in 22％crude protein diets but improved AME by 2.92 MJ (14.16 versus 11.24 MJ;P<0.001) in diets containing 17％crude protein. Ileal N digestibility was greater in broilers offered diets with 17％crude protein than those offered the 22％crude protein diet;irrespective of phytase and pre-pellet cracked maize. Conclusion:Pre-pellet cracked maize and phytase inclusions will improve the performance of broilers offered reduced crude protein diets.