The electrodeposition mechanisms of 3,4,-ethylenedioxythiophine (EDOT) were studied according to electrocrystallization theory. The analyis of the chronoamperograms indicated that the initial stage of the electrodeposition was a combination of instantaneous 2-D and instantaneous 3-D mechanisms since the electrodeposition was carried out under charge transfer control rather than diffusion. In the later stages, layer-by-layer growth mode in accordance with the Stranski-Krastanov model was observed. Our results shown a variation of the anodic transfer coefficient as a function of monomer concentration. Under our experimental conditions, the growth rate constant of the 2D nucleus and the growth perpendicular to the surface rate constant did not depend upon potential beyond a monomer concentration of 0.15 mol l(-1). The quasi-metallic behaviour of oxidized poly(3,4-ethylenedioxythiophene) (PEDOT) was analyzed according to Feldberg's model. A Feldberg parameter of 0.61 V-1 was obtained. The stability of PEDOT was studied during successive polarization between - 0.6 and 0.5 V at a scan rate of 0.2 V s(-1) in acetonitrile and in aqueous solutions containing tetrabutylammonium perchlorate and lithium perchlorate as electrolyte. About 86 and 66% of the electrochemical activity were retained after polarization for 1200 cycles in acetonitrile and aqueous solutions, respectively. These results indicated the good stability of the thin film of PEDOT on the electrode surface.