We present new results on supported palladium based nanocatalysts prepared by water-in-oil microemulsion, which leads to highly dispersed nanoscopic catalysts. Physicochemical methods were used to characterize the compositions (TGA-TDA), the crystallites (XRD) and the particles size (TEM). Different compositional ratios of Pd modified either by silver or by nickel have revealed rather the presence of solid solutions of bimetallic materials which had diameters smaller than 5 nm. They were investigated as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium. The decrease in the noble metal (Pd) content did not sensitively affect the activity of the bimetallic catalyst. Actually the number of electrons exchanged was an almost four-electron-reduction process of oxygen. (C) 2013 The Electrochemical Society. All rights reserved.