A new kind of membrane was prepared by blending cellulose acetate butyrate with cellulose acetate propionate. The properties of this membrane were evaluated by the pervaporation separation of ethyl tert-butyl ether and ethanol mixtures. The experimental results showed that the selectivity and the fluxes of this membrane depend on the blend and on that of processed feed mixtures. With respect to temperature, the overall and the ethanol fluxes obey the Arrhenius equation. The total and the ethanol fluxes increase with the increase of the cellulose acetate butyrate content in the blended membrane, the ethanol concentration in the feed and the experimental temperature. But the selectivity decreases as the cellulose acetate butyrate content in the membrane and the experimental temperature are raised. When the feed composition is varied, the lowest selectivity is observed in the vicinity of the azeotropic composition. The swelling and the sorption experiments also gave the same results.