Blend membranes of chitosan and N-methylol nylon 6 were prepared by solution blending. Their pervaporation performances for the separation of ethanol-water mixtures were investigated in terms of acid (H2SO4) post-treatment, feed concentration, blend ratio and temperature. The pervaporation performance of the blend membranes was significantly improved by ionizing with H2SO4. The blend ratio of chitosan and N-methylol nylon 6 plays a different role at feed solutions of low and high water content. At a feed solution having low water content, an increase in chitosan content caused a decrease in permeability and an increase in separation factor. At a feed solution having high water content, the permeability increases with an increase in chitosan content, while the separation factor shows a maximum value around 60 wt% chitosan. It is proposed that extra permeation channels generated from the phase separation boundary between ionized chitosan and N-methylol nylon 6 account for the abnormal temperature dependence of pervaporation performance of the blend membranes.