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 19 d (12 d for adaptation and 7 d 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: 605 μm), and (c) a basal diet with 20% fine wheat bran (FWB; particle size: 438 μm). The results demonstrated that the apparent total tract digestibility of neutral detergent fiber, acid detergent fiber and energy were reduced (P