A series of Au-Pd nanoparticles (NPs) were prepared using mixed n-dodecylamine/tetraoctylphosphonium bromide ligands and characterized with UV-Vis absorption, TEM, X-ray absorption. ne structure (XAFS), XAFS simulations, X-ray photoelectron spectroscopy (XPS) and catalytic hydrogenation reactions. Enriched Au core-Pd shell structures were found for the 75% and 50% Au NPs and a cluster-on-cluster structure was identified for the 25% Au NPs. Alloy-structure-dependent electronic behavior (e.g. Au 5d electronic density) and surface properties (e. g. surface reactivity) were revealed for these NPs. The results were consistently accounted for by considering the size, surface and alloying effects of the NPs. (C) 2008 Elsevier B.V. All rights reserved.