Au/Nb2O5 and Au/CeO2 catalysts were studied for the selective hydrogenation of crotonaldehyde, both in liquid (batch reactor, 4 atm, 60 degrees C, solvent: isopropanol) and in gas (flow microreactor, 120 degrees C, atmospheric pressure) phases. Samples were characterized by TPR and XRD and tested for the CO oxidation reaction. Large differences in support reducibility between both catalysts were determined from the TPR results. The XRD and CO oxidation results demonstrated that the gold particles were lower than 5 mu. The dependence of the selectivity towards crotyl alcohol and of the conversion on time on stream was measured. The niobia-supported catalyst was mainly unselective, the selectivity towards crotyl alcohol value being 20% for both liquid and gas phases. The Au/CeO2 catalyst is highly selective in gas phase (78% of selectivity towards crotyl alcohol). Under liquid phase conditions, a high selectivity level was not reached mainly due to secondary reactions. (C) 2007 Elsevier B.V. All rights reserved.