A steel cord for reinforcing a rubber product includes a core consisting of one steel filament and a sheath consisting of a plurality of steel filaments wound around the core. The steel filament of the core alternately having straight portions, whose axes of the straight portions are disposed on one line, and protrusions formed by bending. The peak of each protrusion is disposed outside of the sheath. The steel cord for reinforcing a rubber product is used in a pneumatic tire. The pneumatic tire includes a carcass having a crown portion and having a toroidal shape, a pair of beads over which the toroidal shape extends, a belt layer or belt layers for reinforcing the crown portion of the carcass, and rubber surrounding the carcass, the pair of bead, and the belt layer(s). The steel cord is used in the carcass and/or the belt layer(s).