Complex permittivity spectra were obtained in a wide temperature and frequency range from 20 to 200°C and from 10^-2 to 10⁵ Hz for polydicyclopentadiene resin (PDCPD). For comparison, two epoxy resins, one with a similar glass transition temperature (T_g) to PDCPD and the other with a lower T_g, were used. As a result, PDCPD shows much smaller values of ε_r' and ε_r'' than the two epoxy resins in nearly the whole temperature and frequency range. The differences of ε_r' and ε_r'' between PDCPD and the epoxy resin with a similar T_g are also significant at low frequencies and at high temperatures. The increase in ε_r' is attributable to the accumulation of hetero space charges in front of the electrodes. On the other hand, the increase in ε_r'' is an indication of the increase in Joule heat caused by the enhanced charge transport. Therefore, the experiental results indicate that PDCPD possesses better electrical insulating properties than epoxy resin. Furthermore, analysis using complex electric modulus, which is the inverse of the complex permittivity, has revealed very clearly that both charge transport and dipolar orientation are much more difficult in PDCPD than the two epoxy resins.