Epoxy–ZnO composites are prepared via UV-induced cationic polymerization. Complete unsoluble materials are achieved after 10 min of irradiation. Thermal analyses shows an increase of Tg in the presence of the ZnO attributable to a strong hindrance effect of the polymer chain mobility. Electrical characterization of the cured materials shows the decrease of the real part of permittivity with frequency. Both permittivity and AC conductivity values increase with nanofiller content, especially for the highest contents. This is described as typical behavior of nanocomposites made from polymers and fillers with higher permittivity and conductivity values, in accordance with previous data reported in literature for similar composites.