The polymerization of aniline on the p-Si electrode was investigated by in situ Fourier transform infrared-attenuated total reflection spectroscopy. Results show that the N-H vibrational mode of aniline : in the 3490-3050 cm(-1) range, shifts to lower wave number when the applied electrode potential becomes more positive. There is no benzidine intermediate in this polymerization process. The IR adsorption spectrum of the polyaniline spectrum obtained by the in situ method is similar to that obtained by ex situ IR transmission detection. The mechanism of polyaniline synthesis on the p-Si electrode is discussed.