Abstract: Four kinds of soluble dietary fibers( raw soybean dregs SDF1,enzymatic hydrolysis SDF2,extruded SDF3,extrusion-enzymatic SDF4) were extracted from soybean dregs and their structural and functional properties were investigated using electron microscope,laser particle size analyzer,ultraviolet spectrophotometer,rotary viscomete and in vitro antioxidant Kits. The results showed that the volume average particle size of SDF4 was the smallest of( 39.311 ± 0.657) μm.The surface structures of SDF2 and SDF4 particles were much looser with almost no edges.SDF4 exhibited the lowest viscosity,stronger cation-exchange and cholesterol-adsorption capacity. The FRAP,the inhibition capacity on ABTS+·and·OH radical of SDF4 was the largest of( 0.169 ± 0.004) mmol/g,( 0.806± 0.028) mmol/g and( 305.739 ± 4.965) U/m L,respectively.Extrusion-enzymatic hydrolysis had a significant impact on the structure and function of soluble dietary fiber( p < 0.05).