In this study, atmospheric plasma treatment has been used to modify the wetting properties of ethylene-methacrylic acid sodium ionomer. The effects of the plasma treatment on surface properties of this ionomer have been followed by contact angle measurements, Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). With the use of these techniques, the overall effects on activationfunctionalization and surface topography changes have been determined in terms of the processing parameters of the atmospheric plasma treatment (rate and distance). The obtained results show a remarkable increase of the wetting properties and optimum balanced behavior is obtained for atmospheric plasma treatment with a rate of 100 mm/s and a distance of 6 mm; in this case, surface free energy is increased from 33 mJ/m(2) (untreated ionomer) up to 62 mJ/m(2), maintaining good transparency. POLYM. ENG. SCI., 52:2573-2580, 2012. (C) 2012 Society of Plastics Engineers