Biodegradable soy protein isolate (SPI), containing 2,2-diphenyl-2-hydroxyethanoic acid. films (SB) were successfully prepared with bis-(2-hydroxyethyl)sulfide as a plasticizer by compression molding at 155 degrees C and 15 MPa. By immersing the SB in distilled water for 26 h, we prepared the films (coded as SB-WM) having good water resistance. The films were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermoravimetric analysis, dynamic mechanical thermal analysis, and tensile testing to evaluate their structure and properties. Moreover, the surface of the SB-WM films was analyzed by X-ray photoelectron spectroscopy and contact angle measurement. SB-WM films exhibited significantly higher contact angle than SB. The results revealed that a lotus-like nanoscale structure was created in SB-WM films. with increased hydrophobicity. through the process of the solvent-induced microphase separation during the immersion in water. More stable compound diphenylhydroxymethane could form from 2,2-diphenyl-2-hydroxyethanoic acid of SB in water, leading to the hydrophobicity of the SB-WM materials. A "green" and easy method for fabricating hydrophobic materials from soy protein has been provided in this work.