Poly (vinyl alcohol) (PVA) and cellulose acetate (CA) are widely used as membrane materials. Here PVA/CA blended membranes were prepared over a range of 0-100 wt% CA loading, and applied to separate water-ethanol and methanol-methyl tert-butyl ether (MTBE) mixtures by pervaporation. They were characterized by tensile strength testing, contact angle metering and wide angle X-ray diffraction (XRD), scanning electron microscopy (SEM) and positron annihilation lifetime spectroscopy (PALS). Phase separation was observed from the membrane cross-section. As the CA loading increases, the radius of free volume cavity and fractional free volume of the blended membranes increase simultaneously. The as-prepared blended membranes exhibit good separation performance in pervaporation of water (15 wt%)-ethanol and methanol (15 wt%)-MTBE mixtures. Blending has improved permeability of the PVA membrane and selectivity of the CA membrane. The total flux greatly increases whereas separation factor falls with increasing CA loading. The permeances of water and methanol are higher than 8000 gpu and continually increase with CA loading. The results will provide guidance and reference for designing high efficient polymer blended membranes. (C) 2013 Elsevier B.V. All rights reserved.