A steel cord for a tire which increases a corrosion resistance and durability and improves the energy efficiency during curing of the tire and a radial tire using the same. This steel cord has an mnulln twist structure comprising a core containing m pieces of wires and a sheath containing n pieces of wires, in which a rubber compound or an elastomer compound is filled into a space between the core and the sheath. Otherwise, the steel cord has a 1nullN twist structure containing N pieces of wires, in which a rubber compound or an elastomer compound is filled into a space at a cord center surrounded by the N pieces of wires.