A simple electrochemical method for the in situ preparation of homogeneously dispersed gold-polyaniline core/shell nanocomposite particles with controlled size on the highly oriented pyrolytic graphite (HOPG) was demonstrated. The HOPG surface was modified preferentially by covalent bonding of a two-dimensional 4-aminophenyl monolayer employing diazonium chemistry. AuCl4- ions were attached to the Ar-NH2 termination and reduced electrochemically. This results in the formation of Au nuclei that could be further grown into gold nanoparticles. The formation of polyaniline as the shell wrap of Au nanoparticle was established by localized electro-polymerization. These core–shell nanocomposites prepared were characterized by AFM and cyclic voltammetry. The results show that the gold-polyaniline core-shell composites on HOPG have a mean particle size of 100 nm in diameter and the polyaniline shell thickness is about 15 nm.