Abstract <p>In this study, petroleum resin was employed to enhance the hydrophobic properties of polyethersulfone (PES) membranes. Composite membranes, namely C5/PES and C9/PES, were fabricated by blending varying ratios of C5 and C9 petroleum resins with the PES casting solution. The results demonstrated that the incorporation of petroleum resin significantly increased the membrane contact angles. Specifically, the C5/PES (5 : 2) and C9/PES (1 : 1) composite membranes exhibited contact angles of 114° and 116°, respectively, indicating excellent hydrophobic characteristics. Furthermore, the addition of hydrophobic nanoparticles, such as Al₂O₃ and SiO₂, further enhanced the membrane’s hydrophobicity. Notably, the Al₂O₃-modified membrane achieved a contact angle of up to 131°. Experimental results also revealed that the combined modification with petroleum resin and nanoparticles substantially improved the hydrophobicity of various commercial hydrophilic membranes, including nylon, PES, and MCE, as well as PP and PTFE that had been hydrophilized during commercial processing. These results highlight the potential of the modified membranes for use in membrane distillation, gas-liquid separation, and related separation processes. In conclusion, the synergistic modification using petroleum resin and nanoparticles provides an efficient strategy for enhancing the hydrophobicity of organic membranes, providing technical support for potential applications.</p>