Fresh and one-year-old thin polyaniline films prepared during the in-situ precipitation and dispersion polymerizations of aniline hydrochloride on gold and silicon supports in forms of emeraldine salt and base were characterized by UV-visible, Fourier-transform infrared, and Raman spectroscopies. Raman microscope has been used for the analysis of molecular structure. It has been shown that the films prepared by dispersion polymerization are thinner and more resistant to heating. In all cases, the films prepared on silicon were more stable against aging in air than those prepared on gold, which are, on the other hand, more stable against chemical deprotonation. The role of aniline oligomers adsorbed in the early stages of aniline oxidation on the silicon and gold substrates in the molecular structure and stability of the films has been discussed. (C) 2011 Elsevier B.V. All rights reserved.