Abstract: To utilize wheat bran by-products in high value, wheat bran raw materials were pretreated with ultrafine grinding (for 0, 10, 20, and 30 min) and wheat bran polysaccharide was obtained by water extraction and alkali extraction. The effects of ultrafine grinding pretreatment on the physicochemical properties of wheat bran polysaccharides were analyzed based on yield, chemical composition (arabinoxylan, total sugar, protein, and ferulic acid), infrared spectrum, monosaccharide composition, potential, particle size, solubility, and microstructure. The results showed that the yield of alkali-extracted and water-extracted wheat bran polysaccharide increased from 6.6% and 1.34% to 15.03% and 6.28%, respectively. The content of arabxylan (AX) obtained by alkali extraction and water extraction increased from 53.13% and 33.32% to 73.35% and 37.52%, respectively. The particle size of alkali-extracted and water-extracted wheat bran polysaccharide decreased from 308.47 and 919.23 nm to 203.8 and 168.03 nm, respectively. The results from infrared spectroscopy and monosaccharide composition analysis showed that the ultrafine grinding pretreatment had little effect on the structure of the functional group of polysaccharide extracted from wheat bran by alkali and water extraction. However, the pretreatment could destroy the ordered structure of the wheat bran polysaccharide. The total content and proportion of arabinose and xylose, which were the main components of wheat bran polysaccharide, increased significantly after ultrafine grinding (P<0.05). The scanning electron microscopic (SEM) data showed that the particle shape of the polysaccharide changed from large to small and there was high adhesion between polysaccharide. Taken together, the ultrafine grinding pretreatment can improve the yield of wheat bran polysaccharide and enhance the content of Arabxylan, while reducing the particle size of the polysaccharide.