Polymers such as polyethylene (PE) have a low surface free energy and therefore often require a modification of their surface properties before any use. Nonthermal plasma treatment is a convenient and environmentally friendly way to obtain these modifications by introducing new chemical groups at the surface without affecting the bulk properties. Therefore, in this article, a PE film is treated with a dielectric barrier discharge (DBD) operating in air at medium pressure (5.0 kPa). The surface properties of the plasma-treated PE films are characterized using contact angle measurements, surface free energy calculations and ATR-FTIR spectroscopy. The polymer films show a remarkable increase in surface free energy after plasma treatment. ATR-FTIR spectroscopy of the plasma-treated PE films reveals that plasma treatment introduces oxygen-containing functionalities, such as ketones, aldehydes, alcohols and carboxylic acids on the PE surface leading to the increased surface free energy. Copyright © 2008 John Wiley & Sons, Ltd.