PURPOSE: To improve anti-corrosion and anti-fatigue characteristics of a steel cord used at least for either a belt or a carcass by bettering the pearlite structure of the filament of the basic line for the steel cord.

CONSTITUTION: In case of a radial tire with its carcass reinforced by a belt integrated in the inner side of a tread and with at least either its carcass or the belt using steel cord, the steel cord used is limited to the one with its metallic organization in a pearlite constitution with an average cementite lamellar interval in the range between 300W500 Angstrom. Also the pearlite crystal should have a micro-structure of an average cross section below 20μm2 for its own one filament and the tensile strength over 220kg/mm2. The basic line consisting of the filament with above specifications is to be intertwined into a twisted line for the use as the steel cord.