The present study is entirely devoted to an XPS analysis of (i) the surface of as received and plasma (argon, CO,) treated poly(methyl-methacrylate) (PMMA) and (ii) the interface between PMMA and alumina thin films, deposited by r.f. magnetron sputtering respectively on untreated and CO2 plasma-treated polymer films. As expected, important chemical modifications of PMMA surface are observed when this polymer is plasma-treated. Such modifications increase the level of interactions between alumina and the substrate. However, if the formation of aluminium carboxylate is observed at the interface, no covalent bonds between the alumina film and the polymer are evidenced.