Dielectric and electrical properties of radiation-cured epoxy are investigated in various conditions of electric field and temperature for different initiator content. The impact of the onium salt initiator is particularly considered due to the formation of ionic species that can impact the electrical properties. Dielectric spectroscopy performed in the temperature range -80 °C to +200 °C and the frequency range 10 -1 to 10 6 Hz shows that β-relaxation of the cured resin and relaxation due to ionic species are dominating the dielectric behavior at low and high temperature respectively. Water absorbed in the resin increases the dielectric losses and conduction current. Ionic and electronic charge carriers are seen to dominate the electrical behavior at low and high field respectively. No clear trend has been observed as regard the effect of initiator concentration on the dielectric and electrical properties of radiation-cured epoxy.