Copper nanoparticles have been prepared by the reduction of copper(II) sulfate in an aerated water using sodium borohydride at room temperature and stabilized by inorganic anion. Mechanistic steps for the stabilization provided by iodide anion was studied using pulse radiolysis technique. Various inorganic anions have been used to stabilize Cu nanoparticles and compared for their stabilization efficiency. The synthesized nanoparticles exhibit a distinct absorption maximum in the region 560-565 nm. The average size as estimated from TEM micrographs has been found to be in the range 8-10 nm. (C) 2002 Elsevier Science B.V. All rights reserved.