PURPOSE: To produce a pneumatic radial tire improved in durability by winding a spiral filament around a core cord with a specified pitch and burying the resultant steel cords in a rubber layer such as carcass layer.

CONSTITUTION: This steel cord is produced by conducting layer twisting of three core filaments (f1) having 0.23mm wire diameter to prepare a core cord (c), twisting a sheath filament (f2) having 0.23mm wire diameter around the outer periphery of the core cord (c) to form a layer-twisted cord having sheath layers composed of an inner layer (s1) and an outer layer (s2) and winding a spiral filament (p) therearound with a winding pitch within a range of 6 to 20mm. The produced steel cord is improved in strength and fatigue resistance. A pneumatic radial tire is produced by burying the steel cords in a rubber layer having 40 to 70kgf/cm2 100% modulus, e.g. carcass layer.