We investigated the effects of finely ground wheat bran on the nutrient digestibility, digesta passage rate, and gut microbiota structure in sows. A 3×3 Latin square design with 3 test periods and 3 experimental diets was used. Six non-pregnant sows (parity: 5 to 7) were randomly assigned to 3 experimental diets with 2 replicates per treatment in each period. Each period lasted 19d (12d for adaptation and 7d for experiment). The experimental diets included (a) a basal corn and soybean meal diet (CON), (b) a basal diet with 20% coarse wheat bran (CWB; particle size: 605μm), and (c) a basal diet with 20% fine wheat bran (FWB; particle size: 438μm). The results demonstrated that the apparent total tract digestibility of neutral detergent fiber, acid detergent fiber and energy were reduced (P<0.05) in the FWB and CWB groups compared with those in the CON group. Viscosity of digesta increased (P<0.001) in FWB-fed sows. The passage rate of digesta from the mouth to the ileum decreased (P<0.001) in FWB-fed sows. Peptide YY (PYY) concentration increased (P=0.01) in FWB-fed sows after 30min of feeding. In the FWB group, the relative abundance of Lactobacillaceae at the family level increased (P<0.05) in the ileal digesta. At the class level, the relative abundance of Clostridia in feces decreased (P<0.05) in FWB-fed sows. FWB enhanced the concentration of butyrate in feces compared with CON and CWB (P=0.04). These results suggest that dietary supplementation with finely ground wheat bran reduces the passage rate of digesta, increases the abundance of beneficial microorganisms, and elevates the concentration of short-chain fatty acids and PYY in sows. These findings indicate that the addition of finely-ground wheat bran to the diets of sows is more effective than using coarse wheat bran for improving their satiety and intestinal microbial composition.