A high-purity cycloaliphatic diepoxy compound of General Formula (II) is an epoxidized product of a cycloaliphatic diolefinic compound of General Formula (I) having an isomer content as detected in gas chromatography (GC) of 15% or less: wherein X represents a bivalent group selected from the group consisting of, for example, O, S, —SO—, —SO2—, —CH2—, and —C(CH3)2—; and R1 to R18 may be the same as or different from each other and each represent hydrogen atom, a halogen atom, a hydrocarbon group which may contain oxygen atom or a halogen atom, or an alkoxy group which may be substituted. Such a high-purity cycloaliphatic diepoxy compound is prepared by producing the cycloaliphatic diolefinic compound through distillation, epoxidizing the compound with an aliphatic percarboxylic acid containing substantially no water, carrying out desolvation, and further purifying the epoxidized compound through distillation.