Both electric and electronic apparatus have recently been improving in size and performance with increasing heat quantity from inside and have large and important subjects to diffuse the heat efficiently in their design. Although resins are mainly used for insulating materials, they have quite low thermal conductivities, usually 1 - 3 orders lower than those of ceramics and metals, to greatly prevent the heat from diffusing. In this paper, we suggested a novel strategy to afford high thermal conductive thermosetting resins and confirmed it. We used several kinds of epoxy resin monomers with mesogens, and cured them with aromatic diamine curing agents. The thermal conductivities of epoxy resins containing biphenyl groups were 0.22 - 0.33 W/m·K that were a maximum 1.7 times higher than the conventional epoxy resin of 0.19 W/m·K, but the values were considered to be a limit in this system. To further improve the thermal conductivity, we made epoxy resins from the monomers containing two phenyl benzoate groups as mesogens. These epoxy resins had quite excellent thermal conductivities of 0.85 - 0.96 W/m·K that would be highest of all isotropic insulating resins. We also carried out the confirmations of high order structures of resins by TEM observation.