Polyindole can be obtained after anodic oxidation of indole C8NH7 in acetonitrile - LiClO4 Or LiBF4 solutions. This electroactive material presenting an electrical conductivity close to 10(-1) S.cm-1 is green in the doped state and yellow in the reduced form. The behavior of this polymer during prolongated doping-dedoping cycles has been examined : between -0,5 and 0,9 V versus standard calomel electrode, the green to yellow colour change can be observed over more than 450 000 redox cycles. For oxidizing potentials higher than 0,9 V, the irreversible degradation, of polyindole results in the decrease of the electrical conductivity and in the loss of its electrochromic properties.