Abstract: The formation of polypyrrole film on electrode surfaces by anodic-oxid-tion polymerization was studied using Pt foil as substrate.An uiform and seemingly transparent film of polypyrrole with remarkable electro-chromic feature can be obtained under suitably controlled conditions. Newly formed polypyrrole films exhibit activity toward electro-oxidation-reduction in certain electrolytes,but they gradually tend to be inactive and of high resistance on prolonged cyclic polarization. An attempt to apply polypyrrole film forprotecting sintered n-CdS photoanode from photo-corrosion has so far been unsuccessful.