In this work, the strong influence of the anion on both electropolymerization and redox processes of poly(5-amino 1-naphthol) (poly(5-NH2 1-NAP)) is studied by using electrochemical quartz crystal microbalance (ECQM) and atomic force microscopy (AFM). Studies were carried out in the presence of different acid eletrolytic solutions: hydrochloric acid (HCl) and camphorsulphonic acid (HCSA) to investigated the role played by anions taking into account the very different characteristics of chloride and camphorsulfonate anions such as size, ionic mobility, charge/mass ratio, etc. The electropolymerization process of poly(5-amino 1-naphtol) leads to the formation of adherent and electroactive films but the electroactivity depends on the chemical nature of the counter anion used in the electropolymerization and electrochemical studies. Charge compensation during redox processes occurs by mainly the expulsion/insertion of protons from the polymeric matrix during oxidation/reduction but the participation of anions cannot be neglected and it plays a relevant role in film electroactivity. (C) 2003 Elsevier Ltd. All rights reserved.