The experiment was conducted to study the effects of corn grains particle size on the gastrointestinal physiology and feed passage rate of laying hens fed corn-soybean diet. A total of 774 pink-shell Lohmann commercial laying hens of 38 weeks old were randomly allocated by laying rate to 3 treatments with 6 replicates per treatment and 43 hens per replicate. The 3 treatments differed only in corn grains particle size (coarse: 1 001.70 μm, medium: 824.97 μm and fine: 671.56 μm). The experiment lasted for 16 weeks. In the end, one hen from each replicate was killed and gastrointestinal samples were taken; another one from each replicate was chosen for a 24 hours’ trial to determine the effect of corn grains particle size on feed passage rate in hens. The results showed that: 1) hens fed coarse corn had a significant lower ulcer score of gizzard than those fed fine corn (P<0.05); 2) corn grains particle size had no effect on crypt depth, villus height and villus/crypt ratio of duodenum (P>0.05), but hens fed coarse corn had significant higher wall thickness (P<0.05) than those fed fine corn; 3) corn grains particle size had no effect on Lactobacillus and Bacillus bifidus concentration while the fine corn group had a significant lower E. coli concentration compared with the coarse corn group (P<0.05); 4) as corn grains particle size decreased, the relative recovery rates of fecal Cr2O3 at 2, 4 and 6 h were significantly increased (P<0.05), but were significantly decreased at 10, 12 and 16 h (P<0.05). Cumulative recovery rate of fecal Cr2O3 was significantly increased at 2 h (P<0.05) and very significantly increased at 4 and 6 h (P<0.01) as corn grains particle size decreased, but no significant differences were found at 8, 10, 12, 16 and 24 h (P>0.05). In the condition of this study, it is concluded that the increasing of dietary corn grains particle size can improve gastrointestinal physiology and nutrient retention in gastrointestinal tract of laying hens.［Chinese Journal of Animal Nutrition, 2010，22（5）:1271-1278］