In aqueous solution, under anodic potentials at which water oxidation occurs, the polypyrrole is irreversibly oxidized leading progressively to an insulating material. In this paper, it is evidenced that this overoxidation process is due to the hydroxyl radicals formed during solvent oxidation. Indeed, it is shown that, at open-circuit potential, polypyrrole films are overoxidized in the presence of hydroxyl radicals produce by Fenton’s reagent (H2O2/Fe2+). On the contrary, the use of hydroxyl radical scavengers, such as methanol and dimethylthiourea, allows one to increase the stability of polypyrrole films under anodic potentials.