In this study, the surfaces of poly(ethylene terephthalate) (PET) films have been modified by high density inductively coupled plasma (ICP) using the oxygen gas. The ICP-modified PET surfaces have been characterized by atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurement as a function of RF power applied to ICP antenna. The experimental results reveal that the exposure of PET films to ICP leads to the roughening surface and the increase of oxygen containing-functional groups such as O-C=O and C-O at the surface. Also, the contact angle of distilled water on the surface decreases with increasing RF power, resulting in the increase in the adhesion energy.