xChitosan composite membranes having a microporous polysulfone substrate were prepared and tested for the pervaporation dehydration of aqueous isopropanol mixtures. When the composite membrane experienced excessive swelling at the feed mixture of high water content, the composite membranes were found to be segregated in structure due to the opposite characteristics to water of chitosan and polysulfone. Efforts to enhance the structural stability under various pervaporation operational conditions were made. The polysulfone substrate was immersed into hydrophilic binding polymer solutions such as polyvinyl alcohol, polyacrylic acid, and hydroxyethylcellulose before the casting of chitosan layer to increase the affinity between the thin chitosan layer and porous polysulfone layer which resulted in increased geometrical stability of the chitosan/polysulfone composite membranes. The chitosan layer was crosslinked with glutaraldehyde and H2SO4 in acetone solution to control the permselectivity.