Composite membranes consisting of an active alginate layer and supporting chitosan layer on top of the base porous blended polyvinylidene fluoride (PVDF) membrane were prepared and tested for pervaporation dehydration applications. Efforts to enhance the surface properties of PVDF by blending with relatively hydrophilic polymethyl methacrylate (PMMA) were carried out and evaluated by contact angle measurements. Various modifications for the alginate/chitosan composite membranes such as converting to the free acid form and cross-linking with cobalt ion;were investigated. They were then compared for the pervaporation dehydration of ethanol/water and isopropanol/water mixtures and the temperature effect on the permeation flux was also investigated.