The oxidative polymerization of aniline was investigated using H2O2 as an oxidant and metallic gold as a catalyst. In the form of colloidal nanoparticles, gold produces the conductive polyaniline only in a low yield, whereas when supported on carbon and titania, it improves the polymerisation reaction. For an Au/TiO2 catalyst, a synergistic effect between the metal and the support has been demonstrated that allows the production of polyaniline at high yield (70%). Morphological aspects, derived by TEM and SEM techniques, allow identification of the polymeric material in form of nanospheres 45–600 nm in diameter.