Dispersions of Ag, Pd, and Pt-Ru alloy nanoparticles in poly(vinylpyrrodione) (PVP) were produced by gamma-irradiation induced reduction of metal ions at room temperature. The photographs from Atomic Force Microscopy (AFM) inform that Ag, Pd, and Pt-Ru alloy nanoparticles were dispersed with the particle sizes of about 25 nm, 0.6-1.5 run, and 15 mn, respectively, in the aqueous dispersions. The nanoparticles of metals (Ag, Pd) and alloy (Pt-Ru) were also dispersed on single-walled carbon nanotubes (SWCNTs) as supporting materials using gamma-irradiation at room temperature. Of interest, the allachment of the nanoparticles onto SWCNTs was strong enough to be present even after chemical cleaning and ultra-sonication. FT-IR spectroscopy gives evidence for the surface modification of SWCNTs through the presence of characteristic peaks of carboxyl and hydroxyl groups and provides support for the dispersion of nanoparticles on the surface of SWCNTs. (C) 2004 Elsevier B.V All rights reserved.