In a weak basic, weak acidic or neutral water-alcohol solution, silver nanoparticles were generated by the reduction of Ag+ ions in the present of colloidal silica. Silica as a substrate played an important role in the formation of Silver particles. The plasmon band of silver particles supported on the surface of silica was considerably shifted to longer wavelength compared with the pure silver sol. The shift in absorption spectra was explained in terms of surface effects induced by the interaction of silver and silica, as well as size effects and irregular shape. (C) 2004 Elsevier B.V. All rights reserved.