A permanent modification of Pt and Au electrode surfaces was observed after the oxidation of pure neutral or acidic ethylenediamine (EDA). Platinum and gold were coated by an organic compound strongly tied through oxygen atoms to metal atoms. The presence of water is of importance : the larger the water concentration the less stable the coating. This phenomenon was studied by coupling electrochemistry, in situ EQCM and ex situ XPS chemical analysis for Pt.