This paper deals with the study of different microporous ceramic membranes used as separators in electrochemical reactors to treat the activating solutions coming from the electroless plating of polymers. The main component of these solutions is Sn(IV) in HCl as diluting agent, then, the effect of the complex species formed between Sn4+ and Cl- ions on the electrical properties of the membranes has been studied. The porosity of the membranes was modified by changing the manufacturing pressure, P, 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 were 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 was less uniform and becomes bimodal with two different characteristic pore diameters. Independently of the manufacturing pressure and the starch percentage, for the rinse water solutions is convenient to keep low concentrations of Sn(IV), since higher values of the effective electrical conductivity of the membrane were obtained, whilst for treating the activating-wasted baths is better to maintain concentrations of Sn(IV) lower than 0.1 M in order to reach high values of the effective electrical conductivity of the membrane. (c) 2008 Elsevier B.V. All rights reserved.