X-ray photoelectron spectroscopy (XPS) was used to investigate the interface formed between thermally and plasma neared polyparaphenylene-vinylene thin films and an aluminium layer deposited on them. Enhancement in adhesion of the metal on thermally treated polymer films is explained by the structural change of aluminum layer. In contrast, plasma treatments induce morphological modifications of the polymer surface and favor the formation of compounds between the polymer and the metal which in turn improve the adhesive strength.