The phenomenon of the large overpotential at the first reduction of the as-prepared polypyrrole perchlorate films in propylene carbonate (PC) solutions was studied by cyclic voltammetry, chronoamperometry, in situ Vis-NIR absorption spectroscopy and scanning electron microscopy (SEM) etc. It was found that the structure and morphology of the films changed dramatically and the films expanded obviously after the first reduction/re-oxidation cycle of the cyclic voltammetry. The overpotential phenomenon is sensitive to the water content in the electrolyte solution where the cyclic voltammetry was performed. The mechanism of the first reduction was discussed.