Abstract: The conducting polymer, polyparaphenylene (PPP), can be electrochemically polymerized in concentrated sulphric acid. The iu-situ ESR experiment shows that the PPP film possesses high conductivity and low spin susceptibility. Polarons and bipolarons are the main conducting species and interchange each other according to the electrode potential.The unpaired spins are highly delocallized.There may be some interchain O-bridges existing in the PPP film. The bridged structure may produce a space effect, which make the film easily doped and increase the conductivity through interchain charge hopping. In conc. H_2SO_4, the electrochemical intercalation of HSO~-_4 ions is reversible. The doping capacity can be as high as 22%, implying one positive charge in every 5 benzene units. It is possible to use this polymer as stable electrode material for secondary battery.