The surface modification of poly(ethylene terephthalate) (PET) and UV-cured tripropyleneelycol diacrylate (acrylic) films induced by remote N-2 and Ar microwave plasmas (2.45 GHz) was compared by in-situ! XPS measurements. Both N-2 and Ar plasma treatments led to destruction of the initial oxygen-containing groups. The destruction of ester groups was much faster fur the acrylic than for the PET film, and the destruction of ether groups was much faster than that of ester groups within the acrylic Blm. Among the plasma Eases, N-2 was more effective than Ar in the cast: of PET, but their difference was negligible in the case of the acrylic film. The higher stability of thc PET surface was attributed to the presence of a rigid aromatic backbone, which protected the ester groups from plasma UV irradiation and stabilized the free radicals. The lower stability of the acrylic film was associated with the presence of weak ether groups. New functional groups were created, attributed to carbonyl in the case of Ar, and carbonyl/amide and amine in the case of N-2 plasma treatments. The Formation of these new Functional groups was very small compared with the loss of ether and ester groups, suggesting that the destruction of these oxygen-containing groups proceeded mainly through elimination of the entire groups.