We report the fabrication of stable Au nanoparticle/polyoxometallate modified glassy carbon electrodes using layer-by-layer (LbL) assembly. These hybrid films were formed by the sequential deposition of poly(diallyldimethylammonium) chloride (PDDA) stabilized Au-nanoparticles (NPs) and transition metal substituted POMs, and were employed as electrocatalysts for the oxygen reduction reaction (ORR). The LbL approach allows the film thickness, metal NP and POM to be varied systematically in order to optimize catalyst performance. Rotating electrode measurements were used to study ORR kinetics at a series of GC/{M-POM/Au-NP}(n) (M = Ru, Co, W) electrodes. POM co-catalysts containing more labile M-O bonds were found to be better ORR co-catalysts than POMs containing more stable M-O bonds. (C) 2011 Elsevier Ltd. All rights reserved.