A solid solution of Pd-Ag nanoparticles was synthesized by the conventional polyol process. Silver nitrate (AgNO3, Aldrich), palladium(II) nitrate hydrate [Pd(NO3)(2)center dot xH(2)O, Aldrich], and ethylene glycol were used as the starting materials. Ethylene glycol was used as the surfactant for the solvent and reductant. Water was used to ensure that the reduction potentials of the two metals remained very similar in the aqueous solution. The obtained alloy nanopowder sample was characterized by X-ray diffraction (XRD). The obtained XRD pattern was refined using the Full-Prof program according to the Rietveld method and the mean crystallite sizes were estimated using the Scherrer equation. The quantitative atomic percentage across the nanoparticles was determined by using scanning transmission electron microscopy images to confirm the formation of the Pd/Ag alloy nanopowder. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3414468] All rights reserved.