Three polyester films with different repeating units-poly(lactic acid) (PLA), poly(ethylene terephthalate) (PET), and poly(oxybenzoate-co-oxynaphthoate) (PBN)-were modified by plasma, and the way in which the chemical compositions of the polymer chains influenced the plasma modification was investigated with contact-angle measurements and X-ray photoelectron spectroscopy (XPS). There were large differences in the compensated rates of weight loss among the three polyester films when they were exposed to Ar and O-2 plasmas. The PLA film showed the highest rate for weight loss of the three films, and the PBN film showed the lowest rate. The PET and PBN film surfaces were modified to become more hydrophilic by either argon or oxygen plasma. However, the PLA film surface was not made more hydrophilic by the plasmas. XPS spectra showed that the PLA film surface was not modified in its chemical composition, but the PBN film surface was modified in its chemical composition to form C-O groups in the PBN polymer chains. The reason that the PLA film surface was not modified but the PBN film surface was modified was examined. (C) 2003 Wiley Periodicals, Inc.