Palladium nanoparticles (4-6 nm) were deposited inside multi-walled carbon nanotubes (MWNTs) via a simple impregnation using an aqueous solution containing a palladium salt. The low surface tension of the solvent allows a complete filling of the tube, leading, after thermal treatments, to the formation of small and homogeneous palladium particles decorating the inner cavity of the support. The impregnation method was extremely efficient as no palladium particle located on the outer surface of the tubes was observed. The catalyst was tested for the selective hydrogenation of cinnamaldehyde which contains both a C=C and a C=O bond. The nanotubes based catalyst exhibits along with a high catalytic activity an extremely high selectivity towards the C=C bond hydrogenation when compared to a commercial catalyst supported on a high surface area activated charcoal. A peculiar metal-support interaction and the absence of micropores and of oxygenated surface groups on the carbon nanotubes support are proposed to explain these results. (c) 2005 Elsevier B.V. All rights reserved.