The industrial use of ethylene-vinyl alcohol copolymer (EVOH) film is limited because it is easily degraded by moisture. The plasma source ion implantation (PSII) technique with CF4 or CH4 gas was used for the EVOH film to improve the surface hydrophobic properties. Variables examined in implantation were ion energy (0-10 keV), treatment time (5 s-5 min), and ion species. The hydrophobic properties of EVOH films were greatly enhanced after a CF4 PSII treatment, as evidenced by an increased contact angle from 66 to above 100degrees at -5 keV, and remained relatively unchanged during the period of 28 days. X-ray photoelectron spectroscopy, atomic force microscopy, and O-2 permeability were used to characterize the surface properties of EVOH films treated with PSII. The improved hydrophobic properties were closely related to the formation of fluorine-containing functional groups such as CF, CF2, and CF, on the modified surface. The percentage distribution of carbon functional groups supports the role of CF2 and CF, groups in surface modification. (C) 2004 Wiley Periodicals, Inc.