Abstract: To enhance the foaming properties of soy protein isolate (SPI), SPI was subjected to ball milling at varying ball-to-material ratios (8:1, 14:1, and 20:1) for 150 min at a rotational speed of 96 r/min, using untreated SPI as a control. Effects of ball milling on the structural and foaming properties of SPI were analyzed by measuring the average particle size, Zeta potential, turbidity, solubility, surface hydrophobicity, and surface free sulfhydryl (-SH) content. The spatial structure and foaming properties of SPI were also evaluated. The results showed that ball milling significantly reduced the average particle size, Zeta potential, turbidity, and surface free sulfhydryl content of SPI (P<0.05), while significantly increasing its solubility (P<0.05). Although ball milling significantly affected surface hydrophobicity (P<0.05), which first increased and then decreased with increasing ball-to-material ratio, no notable effect was observed on the secondary structure of SPI. Consequently, the foam stability and foamability of SPI were significantly improved by ball milling (P<0.05), reaching maximum values of 86.77% and 125.97% at ball-to-material ratios of 8:1 and 20:1, respectively. In conclusion, moderate ball milling treatment can alter the molecular structure of SPI, thereby improving its foaming properties, expanding its use in foam or aerated foods, and enhancing food quality.