Plasma treatment is often used to modify the surface properties of polymer films, since it offers numerous advantages over the conventional surface modification techniques. However, plasma-treated polymer films have a tendency to revert back to the untreated state (aging process). Therefore, the stability of plasma-induced changes on polymer surfaces over a desired period of time is a very important issue. The objective of this study is to examine the effect of storage conditions (relative humidity and temperature) on the aging behavior in air of plasma-treated low density polyethylene (LDPE) films. Plasma treatment is performed using a dielectric barrier discharge (DBD) operating in different argon/water vapor mixtures at medium pressure (5.0 kPa). Results show that the aging process can be suppressed by storing the plasma-modified LDPE films at low temperature and by decreasing the relative humidity of the surrounding air. Adding water vapor in the plasma discharge has a positive influence on the aging process: lower plateau WCA values are found for plasmas containing a higher water vapor concentration and it takes a longer time to reach these plateau values. In this paper, it is also shown that storage first at a lower temperature and then aging at a higher temperature is not able to slow down the aging effect.