Polyparaphenylene (PPP) films were prepared by electrochemical oxidation of benzene in liquid SO2+ CF3SO3H at low temperatures. Characteristic cyclic voltammograms (CVs) with sharp well-separated redox peaks were observed by scanning in H2SO4 (95%). Upon potential scanning between -0.1 V and +0.7 V versus a saturated calomel electrode (SCE) in H2SO4 (95%) at room temperature for several hours, the peaks decreased progressively and finally disappeared, being replaced by broad redox peaks. According to IR and X-ray photoelectron spectroscopy studies, the transformation of the CV was accompanied by dopant exchange and cross-linking. The sharp reduction peak was attributed to the difficult removal of the CF3SO3- anion which was introduced into the PPP film during electrochemical polymerization. When a high potential of +1.2 V/SCE was applied, the sharp redox peaks immediately became broad and ill defined, whereas their intensity decreased gradually without any shift when the potential scan was limited to +0.5 V/SCE.