Polyaniline was synthesized electrochemically from an aqueous solution of aniline containing perchloric acid. The obtained polymer films were treated with an aqueous solution of hydrazine or sodium hydroxide. Otherwise, anodic or cathodic potential were applied to the polyaniline films in an aqueous solution of perchloric acid. X-ray photoelectron spectroscopy (XPS) was utilized to investigate the differences in these various kinds of polyaniline films. A peak which changed its intensity according to the conductivity of the films and the amount of perchlorate ion contained was found at a higher binding energy position than that of the nitrogen photoelectron peak. The scheme of conductive polyaniline proposed by Bredas et al. give a reasonale explanation to these results.