The microstructure, density, and conductivity of Li2SO4 ion-conducting membranes incorporating nano-composite Li2SO4-Al2O3 prepared using a sol-gel technique are superior to membranes having the same bulk composition prepared from mixtures of lithium sulfate and fine alumina powder. Properties of membranes made from the nano-composite material depend on both the overall composition and the preparative parameters. The relationships between preparative parameters, microstructure, and properties have been determined, from which we have found the optimum lithium sulfate content and thermal treatment parameters for manufacture of membranes with minimum gas permeability and maximum ionic conductivity. (C) 2006 Elsevier Ltd. All rights reserved.