Effects of pH of different electrolyte solution systems on the electrochemical activities and stabilities of polypyrrole(PPy), poly(N-methylpyrrole) [poly(N-M.P.)], poly(N-ethylpyrrole) [poly(N-E.P.)], and poly(N-phenylpyrrole) [poly(N-P.P.)] films were investigated. For electrolyte solution systems, used were TBADS/ACN, LiClO4/PC, LiClO4/THF, LiClO4/DMSO, and LiClO4/H2O. The electrolyte solution systems became more basic as the monomers were polymerized and the polymerized films were cycled. The oxidation peak potential was increased and the stability of polymer films was decreased as the pH of the electrolyte solution systems was decreased. It was found that the film surface became less dense when the cycling was done in the strong acidic electrolyte solution systems.