Background: Measures to improve bird performance have been sought due to the imminent phase out of in-feed antibiotics in poultry and continued demand for higher poultry feeding efficiency. Increasing grain particle size and dietary fibre may improve gizzard function, digestive efficiency and nutrient absorption. This study was conducted to evaluate the effect increased particle size of corn and inclusion of sugarcane bagasse (SB) on mRNA expression of genes encoding digestive enzymes and nutrient transporters in broilers. Results: A total of 336 day-old Ross 308 males were assigned in a 2 x 2 factorial arrangement of treatments with corn particle size - coarse 3576 mu m or fine 1113 mu m geometric mean diameter, and SB - 0 or 2\% inclusion. Feed conversion ratio (FCR), weight gain and feed intake were measured from d 0-10 and d 10-24. The relative gizzard weight and mRNA expression of genes encoding digestive enzymes and intestinal nutrient transporters were measured on d 24. During d 10-24, a particle size x SB interaction was observed for FCR (P < 0.01), where birds fed coarsely ground corn (CC) with 2\% SB had lower FCR than those fed CC without SB. A particle size x SB interaction was observed for both expression of pepsinogen A and C (P < 0.01) which were negatively correlated with FCR on d 24. Addition of 2\% SB upregulated pepsinogen A and C only in CC fed birds. Further, 2\% SB also upregulated pancreatic amylase (AMY2A) and intestinal cationic amino acid transporter-1 (CAT1). Inclusion of dietary CC upregulated duodenal amino peptidase N (APN), jejunal alanine, serine, cysteine and threonine transporter-1 (ASCT1), and ileal peptide transporter-2 (PepT2). Conclusion: These results suggest that both SB and coarse particle size modulate expression of genes encoding important digestive enzymes and nutrient transporters and thus are directly related to bird performance. These findings provide insights into the combination effects of dietary fiber and particle size in the future management of broiler feeding.