In this study, we report the first sonoelectrochemical methods to prepare gold-silver alloy nanoparticles with the mean diameter of 5 nm in 0.1 N HCl aqueous solutions without addition of any stabilizer. First, a silver substrate was roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous containing 0.1 N HCl. Silver-containing complexes were found in the solution after the ORC treatment. Then a gold substrate was subsequently roughened by the similar ORC treatment in the same solution containing the silver complexes. After this procedure Au- and Ag-containing complexes were left in the solution. Then the Au working electrode was immediately replaced by a Pt electrode and a cathodic overpotential of 0.6 V from the open circuit potential (OCP) of ca. 0.75 V vs Ag/AgCl was applied under sonification to synthesize Au-Ag alloy nanoparticles. (C) 2004 Elsevier B.V. All rights reserved.