The use of barley in poultry nutrition is limited due to its low energy and high cellulose content, as well as antinutritional factors such as beta-glucan. In this study, the effects of barley-based diets processed in a hammer mill with different sieve diameters (4000 (fine), 5000 (medium) and 6000 (coarse) µm) and enzyme addition (0 and 300 g/ton) on the performance, slaughter characteristics, tibia traits, jejunum morphology, and pancreatic enzyme secretion in broilers (1 to 42nd d) were tested in a 3 × 2 factorial arrangement. A total of 450 one-day-old chicks were distributed into 6 dietary groups of 5 replicates, each containing 15 birds. As particle size increased, final body weight decreased. Feed intake was not affected by treatments. Between 0-10th days, feed conversion ratio increased with medium and coarse particles; however, increased with each increase in particle size between 11–24th days. Enzyme addition improved final body weight, feed intake between 25 to 42nd days and feed conversion ratio between 0 to 10th and 11 to 25th days. Gizzard increased with coarse particles. Pancreatic enzyme activity concentrated with increasing particle size but decreased with enzyme addition to the diet. The coarse particle size enhanced the tibia breaking strength and ash, also these parameters increased with enzyme addition. The jejunum histomorphology negatively affected with increasing coarse particle size and improved with addition of enzymes. The interactions affected body weight, tibia weight, tibia wall thickness, tibia breaking strength, pancreatic enzyme secretion, and jejunum parameters. In conclusion, grinding barley-based diets to coarse particle size negatively affected performance and intestinal development but improved tibia traits, and enzyme addition positively affected all parameters.