In the present work the effect of the nanoscale morphology on the transport of ethanol/water mixtures through SBS block copolymer membranes is reported. In particular, the ethanol selectivity and overall flux can be optimized by varying the nanostructure of the SBS membranes. Membranes with well controlled nanostructure, characterized by AFM and TEM, have been prepared by selecting the casting solvent on the basis of interaction parameters (chi) with polybutadiene (PB) and polystyrene (PS) blocks and the amount of PS in the copolymer. (C) 2011 Elsevier B.V. All rights reserved.