Titania coatings have been deposited on polyethylene terephtalate (PET) by the r.f. magnetron sputtering method in an oxygen-argon plasma from a titanium target and in a pure argon plasma from a titania target. The dependence of the structural properties and the composition of the deposited films on the sputtering pressure and the r.f. power have been studied. In order to improve the adhesion strength between the titanium oxide films and their substrate, various cold plasmas are used to treat the polymer surface. These treatments＇ influence on the adhesion is studied by using the fragmentation test. The best results are obtained with a carbon dioxide plasma. The adhesion of the titania coating on the PET film also depends strongly on the deposition conditions. The highest values are reached when the titanium oxide films are deposited by the reactive sputtering process and when the elaboration parameters combine a total pressure as low as 0.8 Pa and a power density of 2.54 W cm(-2). The titania/PET interface, investigated by XPS, suggests the formation of Ti-O-C bonds in the first stage of the deposition of the titania films obtained by the reactive magnetron sputtering process, while no chemical reaction seems to occur between the PET and the titanium oxide film sputtered under a pure argon plasma.