Three different types of blend membranes based on chitosan and polyacrylic acid were prepared from homogeneous polymer solution and their performance on the pervaporation separation of water-ethanol mixtures was investigated, It was found that all membranes are highly water-selective. The temperature dependence of membrane permselectivity for the feed solutions of higher water content (>30 wt%) was unusual in that both permeability and separation factor increased with increase in temperature. This phenomenon might be explained from the aspect of activation energy and suggested that the sorption contribution to activation energy of permeation should not always be ignored when strong interaction occurs in the pervaporation membrane system. A comparison of pervaporation performance between composite and homogeneous membranes was also studied, Typical pervaporation results at 30 degrees C for a 95 wt% ethanol aqueous solution were : for the homogeneous membrane, permeation flux = 33 g/m(2) h, separation factor = 2216; and for the composite membrane, permeation flux = 132 g/m(2) h, separation factor = 1008. A transport model consisting of dense layer and porous substrate in series was developed to describe the effect of porous substrate on pervaporation performance.