In a 2x2x3 factorial study, the effect of milling technique (hammer vs. roller) with differing particle sizes (fine or coarse) of maize from three sources (Downs, Emerald or Moree) on growth performance, ileal digestibility and intestinal microbial profiles of broiler chickens (from 1-21 days post-hatch) was investigated. A total of 420 day-old male Cobb chicks were randomly allocated to 12 treatments of 5 replicates (seven birds per replicate) in brooder cages set up in an environmentally controlled room. The maize grain was finely ground using a hammer mill or roller mill with a 2 mm screen or coarsely ground through a 4 mm screen. Feed intake up to 7 days of age was higher (p<0.003) on the diet containing finely roller-milled grain than on the coarsely milled grain but no effect found on d21. Live weight was affected by the source of maize (p<0.04). The FCR to d21 was improved (p<0.042) on the Moree maize that was finely roller milled. The relative weight of proventriculus plus gizzard (p<0.01) and liver (p<0.01) were higher in diets containing coarsely milled grain than finely milled grain at 7 but not 21 days. Nutrient digestibility was affected due to maize source (p<0.01) and particle size reduction (p<0.01). These results suggest that fine grinding some sources of maize would be beneficial in terms of improvement in FI, LW and weight of proventriculus and gizzard in early ages as well as nutrient digestibility at a later age.