Insulating and electroinactive polypyrrole (PPy(NaOH)) film can be synthesized by electropolymerization from an NaOH aqueous solution containing pyrrole at a highly positive, potential. The synthesis of this electroinactive PPy(NaOH) was investigated using in situ UV and X-ray photoelectron spectroscopy, and was compared with the irreversible oxidation ("overoxidation") of electroactive PPy under a highly positive potential. Overoxidation made the PPy inactive. However, the formation of PPy (NaOH) started above 0.5 V vs. Ag/AgCl, and the "overoxidation" began simultaneously in the polymerizing solution. Overoxidation with nucleophilic hydroxide ions caused a structural change in the PPy molecule, which destroyed the original pi-conjugated system.