Different microporous ceramic membranes have been investigated to be used as separators in electrochemical reactors. The effect of porosity on the effective electrical conductivity of the ceramic membranes has been studied. The porosity of the membranes has been modified by changing the manufacturing pressure and by the addition of starch to the alumina-kaolin matrix. In the absence of starch the pore size distribution becomes more uniform with the increase of the manufacturing pressure, and lower porosities and average pore sizes are obtained. On the other hand, the porosity and the average pore size increase with the addition of starch to the alumina-kaolin matrix, but pore size distribution is less uniform and becomes bimodal with two different characteristic pore diameters. The effective electrical conductivity of the membranes, kappa(eff), increases with the decrease of manufacturing pressure and with the increase of starch content. The following correlation between the effective electrical conductivity and the porosity has been obtained: f(c) = kappa(eff/kappa) = 0.35 epsilon(1.04), where kappa is the electrolyte electrical conductivity. (c) 2006 Elsevier B.V. All rights reserved.