A cyclic olefin resin composition which includes (A) 35 to 85 parts by weight of a cyclic olefin polymer having a glass transition temperature of 60 to 200° C., (B) 10 to 60 parts by weight of a flexible copolymer, prepared by polymerizing at least two monomers selected from the group consisting of an olefin compound, a diene compound and an aromatic vinyl hydrocarbon compound, and having a glass transition temperature of 0° C. or below, and (C) 5 to 55 parts by weight of a modified polyolefin. The cyclic olefin resin composition further includes, based on 100 parts by weight of total amount of the components (A), (B) and (C), (D) 0.01 to 5 parts by weight of a radical initiator and (E) 0 to 5 parts by weight of a polyfunctional compound having in its molecule two or more radically polymerizable functional groups. The composition can be used as a material for a substrate having low permittivity, low dielectric tangent, low water absorbability, and excellent heat resistance.