A superoleophobic underwater modified electrospun membrane is produced via a novel effective modification method, to overcome the hydrophobicity and fouling propensity of the electrospun polysulfone (PSf) membrane. In which the fabricated PSf electrospun membranes were immersed in different NaOH concentrations (0, 0.1, 0.5, and 1 M) at different temperatures (25, 50, 75, and 100 degrees C) for different time (1, 3, 5, 7 h) to produce 64 modified membranes. Based on the characterization of the modified membranes, the best-modified membrane was chosen and was investigated in the oil-water separation system. More importantly, the best-modified membrane (M64) exhibits underwater superoleophobic feature and it could effectively separate soybean oil and hexane-water mixtures with a superior water flux of 11,865 and 14,016 LMH after the 5th cycle under a gravity-driven process, respectively. Moreover, the membrane possesses remarkable oil-water separation efficiency with more than 99.99% of oil rejection, where soybean oil and hexane content in the filtrate after the 5th cycle were less than 3 and 1 ppm, respectively, which is lower than the acceptable limit of 10 ppm. Also, the modified membrane exhibited antifouling properties with a water flux recovery ratio of 94 and 96.8% after the 5th filtration cycles of soybean oil and hexane-water mixtures. Overall, this study introduces a simple and effective method to overcome the hydrophobicity of the PSf electrospun membrane and enhance the antifouling property.