This paper presents an original approach to prepare the asymmetric sulfonated polysulfone membranes by using wet phase inversion method and their application for dehydrating a water/ethanol mixture by pervaporation. The separation performances of sulfonated membranes were strongly affected by the degree of sulfonation. The substitution degree of sulfonic group enhanced the permselectivity of sulfonated polysulfone membranes. Based on the morphology observation and light transmittance measurement, the degree of sulfonation presented less influence on the membrane formation pathway in wet phase inversion process. The sorption and permeation properties showed that the permselectivity of asymmetric membrane was dominated by the permeate diffusion rather than the permeate sorption in the skin layer. The high performance of pervaporation membrane was achieved by phase inverse method with sulfonated polysulfone. In this investigation, we found that this work is successful to prepare the asymmetric sulfonated polysulfone membranes by using wet phase inversion method and showed the good performance for dehydrating water/ethanol mixture by pervaporation. The similar light transmittance of those casting solutions implied that the polarity change of modified polymer did not strongly affect the demixing behavior. On the other hand, the less demixing time in water bath will be lead to a thin skin layer of sulfonated membranes. Base on the AFM observation, the roughness on the skin layer of sulfonated membranes decreased with increasing the sulfonation degree of polymers. It is indicated that the sulfonation affect the surface s roughness of sulfonated membranes. The substitution of sulfonic group on polysulfone enhanced both of the permeation flux and the separation factor at 90% ethanol in feed. The sulfonated membranes showed well hydrophilic properties and benefit both of their swelling properties and permeate permeation flux. The sorption and permeation measurement showed that the permselectivity of asymmetric membrane was dominated by the permeate diffusion control rather than the permeate sorption in the dense skin layer. The high performance of pervaporation membrane was prepared by phase inverse method by using the polymer sulfonation method.