The Glass Transition Temperature, Tg, was determined on electron beam cross-linked low- density polyethylene, using the dynamic mechanical analysis technique. The measurements were carried out over a temperature range of -170 to -100 deg.C, at frequencies of 0.5, 1.0, 2.0, 5.0 and 10.0 Hz and at an average heating rate of 1.83 deg. C/min. The radiation dose was 50, 100, 150, 200, 300 and 400kGy that corresponded to about a cross-linking degree from 20 to 80%. The experimental results have shown that Tg changed about 10 degrees as a function of frequency but for each frequency the value of Tg remained constant as a function of the irradiation dose. At the fixed frequency of 1.0 Hz Tg had a value of-139.4??0.1 deg. C and the activation energy was 51.2??0.7kJ.mol-1. These experimental results have shown that the presence of a three-dimensional interconnected structures and increase in molecular weight, due to the cross-linking effect, had not affected the Tg value at each frequency. It was expected that these molecular modifications could hinder, in some way, the molecular rotational motion, changing this Tg value.