We report here the first electrochemical pathway to prepare Cl- and Au-containing nanocomplexes of mean diameter 2 nm in 0.1 M HCl aqueous solutions without the addition of any stabilizer. Based on these prepared nanocomplexes, pyrrole monomers can form self-assembled monolayers and further develop orderly spontaneous polymerization (called autopolymerization), which is distinguishable from conventional chemical or electrochemical polymerization, on these nanocomplexes. Furthermore, the prepared polypyrrole (PPy)-coated gold nanoparticles with a core-shell structure can be further treated with sonication for the preparation of Au(0) nanoparticles. This strategy provides another way to fabricate metal nanoparticles without the addition of any stabilizer. (C) 2004 Elsevier B.V. All rights reserved.