Colloidal dispersions of hybrid nanocomposite composed of polypyrrole (PPy) and gold nanoparticles (Au-NPs) or platinum nanoparticles (Pt-NPs) were prepared by a sonochemical method, in which Au ion and pyrrole monomer in an aqueous solution were reduced and oxidized, respectively, by ultrasonic irradiation in the presence of sodium dodecyl sulfate (SDS). The formation of PPy on the surface of AU-NPs or Pt-NPs is confirmed by UV-vis and transmission electron microscopy (TEM) images. (C) 2005 Elsevier Ltd. All rights reserved.