The effects of high concentrations of polar aluminum trihydrate (ATH) molecules on the dielectric relaxations of low-density polyethylene (LDPE) have been studied by dielectric loss (tan delta) measurements in the temperature range from 25 to 370 K. It was found that there are strong effects of polar ATH molecules on alpha and beta relaxation peaks, but no effect on the gamma relaxation peak, which is usually attributed to the localized conformational changes such as crankshaft or kink motion of the main chain in amorphous-phase surface layers of LDPE. Both strong alpha and beta peaks are shifted to lower temperatures with increasing concentration of ATH in the polymer. This behavior of alpha and beta dielectric relaxations of LDPE was related to the morphological changes in the amorphous and the crystal phase of highly doped semicrystalline polymer.