Palladium-tin catalysts were prepared by successive impregnation or co-impregnation onto polyaniline and polypyrrole. The catalytic tests showed that this type of catalyst is active for nitrate reduction. The use of polymer support improves the selectivity of the catalyst toward nitrogen formation compared to a classical support, and avoids the apparition of intermediate nitrite. These better performances of the catalysts supported on electroactive polymers were explained by the ion-exchange properties of the conducting polymers. The most selective catalyst was Pd-Sn/PPy catalyst prepared by successive impregnation. The lower selectivity obtained with the Pani-supported catalyst was explained by the capability of this polymer to directly reduce nitrate into ammonium ions. (C) 2009 Elsevier B.V. All rights reserved.