Polyelectrolyte complex membranes were prepared by simultaneous interfacial reaction of aqueous solutions of two oppositely charged polyions. The cellulose derivative sulphoethylcellulose (SEC) was used as the polyanionic component and poly(diallyldimethylammonium chloride) as the polycationic component. Characterization of molecular parameters of SEC were determined by size exclusion chromatography coupled with light scattering, viscosimetry, and rheology, and then correlated with membrane properties. Pervaporation investigations together with measurements of swelling behavior and network structure indicate that the membranes can be successfully used for dehydration of alcoholic solvents since they show excellent separation properties.