This article reports on the effect of thermal aging oil the electrical properties of crosslinked polyethylene (XLPE) used in high voltage cables. It was shown that thermal aging modifies the electrical properties of the polymer. The degradation is accelerated when the temperature is increased. This,; degradation is due to a thermooxidatiom followed by a loss of antioxidant, and a change ill color of the material. At 80 and 100 degrees C, the antioxidant is practically efficacious,; during the aging, whereas at 120 and 140 degrees C, it is consumed after 1500 and 1000 h, respectively, which results in an increase in the dielectric losses and a diminution in the volume resistivity. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1985-1990, 2009