In this work, AgxPt100-x/C (x = 60, 80, 90 and 95) colloidal nanostructured electrocatalysts for the oxygen reduction reaction (ORR) were prepared by sequential reduction of AgNO3 and H2PtCl6 using an ultrasound-assisted colloidal method. The synthesized materials were characterized by UV/Vis spectroscopy, XRD, EDS and HRTEM. In addition electrochemical measurements were performed using cyclic voltammetry (CV) and thin-film rotating-disk electrode (TF-RDE) technique in 0.5 M H2SO4 at room temperature. Results of the physical characterization showed ring-like morphology of the nanostructured catalyst with a size distribution in the range of 6-16 nm. From steady polarization measurements, the AgxPt100-x/C nanocatalysts showed electrocatalytic activity towards the ORR like that obtained for Pt/C catalyst under the same experimental conditions and also favored the multielectron (n=4e-) charge transfer process to water formation (i.e., O2+4H++4e- → 2H2O).