PURPOSE: To a steel cord for rubber reinforcement improved in durability and working life by forming gaps among the elemental wires for both core strand and outer ply and by making the section of the core strand unidirectionally flat to secure rubber penetrability and corrosive fatigue resistance and effectively decrease wear due to mutual contact among the elemental wires.

CONSTITUTION: In the steel cord for rubber reinforcement having an openly twisted structure made up of (A) core strand formed by mutually twisting two elemental wires 1 and (B) outer ply formed by mutually twisting 6-7 elemental wires 2 around the core strand, gaps are formed among the elemental wires for the core strand and its section 2a is made unidirectionally P flat to the flatness ratio of 1.3 to 2.0, and, in addition, gaps are also formed among the elemental wires for the outer ply; and the outer ply is twisted on the core strand in the identical direction with a longer pitch.