A steel cord is formed by compactly twisting steel filaments together, the steel filaments including a plurality of zigzag filaments and optionally a nonzigzag filament, the zigzag filament being zigzaged two-dimensionally and made up of straight segments each extending between the zigzag peak points, the nonzigzag filament being straight. In case the cord is composed of only the zigzag filaments, the zigzag filaments include at least two kinds of zigzag filaments having different zigzag pitch lengths. In case the cord is composed of both the zigzag filaments and nonzigzag filaments, some of the zigzag and nonzigzag filaments are first loosely twisted together into a bunch, and then a plurality of bunches are twisted together into the cord. In any case, the zigzag pitch length and zigzag wave height of each zigzag filament are substantially constant along the length thereof. A Tire comprises a reinforcing layer such as a tread reinforcing belt layer, carcass, bead reinforcing layer and the like made of the above-mentioned steel cords.