PURPOSE: To obtain a steel cord having plying structure and remarkably suppressing breakage or loose, compared with a conventional cord even if stress is produced in a reinforcing cord in a rubber article and obtain a pneumatic tire using the steel cord as a reinforcing material of a belt layer and improved in durability.

CONSTITUTION: In this steel cord for reinforcement of rubber article having plying structure, obtained by further twisting two or more numbers of strand obtained by twisting ≥2 steel filaments, a diameter RP of a spiral filament used for bundling strands together satisfies the relationship expressed by the formula 0.24≤RP/d [(d) exhibits a distance from a point at which strands maximally approach to the circumscribed circle of the cord].