X-ray photoelectron spectroscopy was employed for thein situstudy of the interactions between thermally deposited Al atoms and polyaniline films of different intrinsic oxidation states. Quantitative changes in the N 1score-level line shape, the evolution of the Al 2pcore-level spectra, and the changes in surface stoichiometry of these films throughout the Al deposition process were carefully tracked. Although the nitrogen sites appear to be more attractive to the incoming Al atoms and the emeraldine and nigraniline films undergo an apparent decrease in intrinsic oxidation state ([=N–]/[–NH–]ratio) as a result of Al deposition, there is no direct interaction between the two species, and the adsorbed oxygen from the bulk of the polymer film plays a dominant role in the interfacial interactions between the polymer and the metal.