The effect of 3 corn particle sizes (dgw: 375, 1117, and 2402 μm) combined with or without organic acids (0.3 g/kg of Galliacid S®) was investigated on broilers from day 1 to day 21; 540 1-day old Ross 708 males were raised in 36 pens (3×2 factorial design, 6 blocks each). We measured: body weight, feed intake, feed conversion ratio, liver weight, pH weight and height of empty gizzard, pH and length of intestine and caeca, height and width of ileal villi, crypt depth/gland diameter, total bacteria count. Different corn particle sizes and organic acid supplements only affected feed intake (days 14 and 21), feed conversion ratio (day 14), villus height, and crypt depth. On day 21, fine milling had negative effects on body weights compared with larger feed particle size (816 vs 848 and 844 g); acidic additive had a positive effect on broiler growth (859 vs 813 g). Length of small intestinal villi and crypt depth were affected by both particle size and organic acids (fine to coarse small intestinal villi: 1869a, 1401c, and 1039d μm in non-acidified; 1708b, 1535c, and 942e μm in acidified. Fine to coarse crypt depth: 102ab, 98b; 65c μm in non-acidified; 106a, 70c, and 66c μm in acidified). No difference was observed in total bacteria counts of the gut in relation to the different treatments. Use of organic acids during starter phase is useful, especially when the milling process is inappropriate. [ABSTRACT FROM AUTHOR]