NOVELTY - A postcure property resin composition comprises ethylene-olefin-polyene copolymers, non-polar vinyl compounds, and hardener. The olefin of the copolymer is 3-20C alpha -olefin, 5-20C cyclic olefin, and/or 8-20C aromatic vinyl compound. The catalyst used when copolymerizing ethylene, olefin and polyene is a single site coordination-polymerization catalyst comprising a transition metal compound (I or II), and a co-catalyst. The non-polar vinyl compounds consist of 5-20C cyclic olefin and/or 8-20C aromatic vinyl compound.    USE - Postcure property resin composition is used for forming hardened component, electrical insulation materials for high-frequency applications, high-frequency integrated circuit interposers, high-frequency integrated circuit underfill materials, multilayer wiring boards, surface coat materials, potting materials, and solar-cell sealing materials (all claimed).    ADVANTAGE - The postcure property resin composition has low dielectric constant, water absorbability, and dielectric loss, excellent softness, dynamic strength, heat resistance, temperature characteristics, water resistance, fluidity, and moldability e.g. film-forming property, and high volume resistivity.    DETAILED DESCRIPTION - A postcure property resin composition comprises ethylene-olefin-polyene copolymers (10-90 parts mass), non-polar vinyl compounds (90-10 parts mass), and hardener. The olefin of the copolymer is 3-20C alpha -olefin, 5-20C cyclic olefin, and/or 8-20C aromatic vinyl compound. The polyene is 5-20C polyene having two or more vinyl groups and/or vinylene groups in a molecule. The copolymer has a number average molecular weight of 1000-50000, a molecular weight distribution of 1.5-5, 1-7 polyene unit content per number average molecular weight, 5-70 mol% of olefin units, and remainder of ethylene units. The catalyst used when copolymerizing ethylene, olefin and polyene is a single site coordination-polymerization catalyst comprising a transition metal compound of formula (I or II), and a co-catalyst. The non-polar vinyl compounds consist of 5-20C cyclic olefin and/or 8-20C aromatic vinyl compound, and have a polyene content of less than 1 part mass.    A,B'=benzoindenyl, indenyl, cyclopentadienyl or fluorenyl (all optionally substituted by 1-20C alkyl, 6-10C aryl, 7-20C alkylaryl, halo, OSiR3, SiR3, or PR2), with at least one being optionally substituted benzoindenyl or optionally substituted indenyl;    R=1-10C hydrocarbyl;    Y'=H or methylene having 1-15C hydrocarbyl (1-3 nitrogen, oxygen, sulfur, phosphorus and silicon atom may also be included), and boron group as substituent, and may have cyclic structure;    X=H, hydroxy, halo, 1-20C hydrocarbyl, 1-20C alkoxy, silyl having 1-4C hydrocarbyl substituent, or amido having 1-20C hydrocarbyl substituent, with two X optionally having a bonding;    M,M'=zirconium, hafnium or titanium;    Cp=cyclopentaphenanthryl, benzoindenyl, cyclopentadienyl, indenyl or fluorenyl (all optionally substituted);    Y"=H, or methylene, silylene, ethylene, germylene, or boron residue having 1-15C hydrocarbyl, and may have cyclic structure;    Z=nitrogen, oxygen or sulfur, and has bond with Y" by ligand coordinated to M' with nitrogen, oxygen or sulfur, or H or group having 1-15C substituent;    X'=H, halo, 1-15C alkyl, 6-10C aryl, 8-12C alkylaryl, silyl having 1-4C hydrocarbyl substituent, 1-10C alkoxy, or dialkylamido having 1-6C alkyl substituent;and    n=1 or 2.