Abstract: The physicochemical properties and structural characteristics of soybean dreg polysaccharides before and after the fermentation with Neurospora crassa were studied in this paper. The fermentation was carried out by Neurospora crassa. Polysaccharides were prepared by water extraction, alcohol precipitation and enzyme-sevag deproteinization. The chemical structures of polysaccharides before and after fermentation were characterized by scanning electron microscopy (SEM), X-ray diffraction, infrared spectroscopy (IR), and gas chromatography-mass spectrometry (GC-MS). The results showed that the content of crude polysaccharides increased by 8.19 times in soybean dregs after fermentation, and the content of total sugar, protein, total flavonoids and total phenols increased. Scanning electron microscopy showed that the polysaccharide of fermented soybean dregs had a larger surface area. X-ray diffraction detected that fermentation had destroyed the crystal structure of the polysaccharides. The infrared spectrum of the polysaccharides showed that both sugars had polysaccharide characteristic absorption peak. After fermentation, the polysaccharide absorption band strength was stronger. The analysis of monosaccharide composition showed that the glucose content was the highest, and the monosaccharide composition was redistributed after fermentation. The thermogravimetric analysis showed that the fermented soybean residue polysaccharides had higher thermal stability. The findings showed that the contents of soybean dregs and the microstructure of polysaccharides were improved after fermentation, which made them have the potential to be used as high quality dietary fibres. It could provide reference for the development of functional food of polysaccharides from fermented soybean dregs.