A steel cord used for reinforcing rubber product with an oval cross-section has a structure of m+n, while m is the number of core wires (26) and n is the number of the outer layer wires (22). The core wire (26) is untwisted while m is 1 or the core wires (26) are untwisted and aligned in parallel while m is between 2 and 4, and the outer layer wires (22) are twisted around said core wires (26). The core wires (26) are oval wires and the outer layer wires (22) are round wires. The wires (22, 26) in the steel cord have a carbon content not less than 0.60%.