Influence of zirconia polymorphism on water-gas shift reaction was investigated. The study was carried out over catalysts with similar features, which allowed assessing any effect brought about by the support crystalline structure. It was found that zirconia polymorphism determines the catalyst activity and the monoclinic structure renders a more active system. It is most likely due to the presence of hydroxyl groups, which have been claimed to be involved in the formation of important reaction intermediates. Catalyst deactivation was also addressed and it could be concluded that the changes in metal phase dispersion along reaction play a quite important role on the ZrO2-supported catalyst stability. (c) 2012 Elsevier B.V. All rights reserved.