Cellulose derived from agricultural by-products as a promising stabilizer for novel food emulsions has been attracting numerous interests. In this work, defatted okara was used to extract insoluble soybean fiber (ISF) under alkaline pH (7.0-12.0). The physicochemical properties of ISF, as well as the formation and stability properties of O/W emulsions (10% w/w of oil) prepared by ISF, were characterized. The results exhibited a lower residual protein content (p < 0.05), as well as a stronger electronegativity and hydrophilicity of ISF, as indicated by -potential and water-in-air three-phase contact angles (theta(wa)) measurements, respectively, as the treating pH increased. ISF extracted at lower pH (<= 10.0) could quickly form O/W emulsions, whereas with little stability. For the emulsions with better stability prepared using ISF extracted at pH 12.0, the storage ability (30 d), and sensitivity regarding pH and NaCl were evaluated. The results revealed that the gel-like network, electrostatic repulsion, and steric hindrance played dominant roles in stabilizing ISF-emulsions. These results will contribute to the development of efficient ISF-based emulsifiers/stabilizers, which may greatly improve the valorisation of soybean by-products.