The effects of steam explosion processing on dietary fiber (DF) in whole soybeans were investigated. Singlefactor steam explosion experiments and response surface methodology were used to optimize modification conditions, and the differences in the structural and physicochemical properties of whole soybean DF were compared before and after modification. The results showed that the optimal process conditions were steam explosion pressure of 1.0 MPa, a holding time of 120 s, and a moisture addition of 100%. Under these conditions, the soluble dietary fiber (SDF) yield increased from 3.22% to 9.51%. The processed insoluble dietary fiber (IDF) and SDF exhibited a looser, more porous microstructure, with water-holding capacity, oil-holding capacity, and swelling capacity of 10.88 g/g, 7.16 g/g, and 9.04 mL/g, respectively. No new vibration peaks were found in the Fourier transform infrared spectra of IDF and SDF before and after the steam explosion. However, the intensity of some peaks varied. X-ray diffraction results suggested that the crystallinity of modified IDF and SDF was 20.79%, which was 14.49% and 18.18% less than that before modification, respectively. In conclusion, steam explosion processing could significantly reduce the IDF content in whole soybeans and improve its physicochemical properties considerably. These findings provide a theoretical basis for developing whole soybean-based functional foods.