Abstract: A steel cord (10) for reinforcing rubber product comprises at least one core strand (12) and outer strands (14), the outer strands (14) are helically twisted around at least one core strand (12). Each of the strands (12, 14) comprises core steel filaments (16, 20) with the number of m and outer steel filaments with the number of n. The diameter of the core steel filaments in the core strand is Dcc, the diameter of the outer steel filaments in the core strand is Doc, the diameter of the core steel filament in the outer strand is Dco, and the diameter of the outer steel filament in the outer strand is Doo. The ratio of Dcc/Doc is not less than 1.04, the ratio of Dco/Doo is not less than 1.03, and the ratio of Doc/Dco is not less than 1. The core steel filaments and outer steel filaments are polygonally preformed before being twisted into strands. The steel cord is used for reinforcing off-the-road tire.