To provide a steel cord capable of developing a satisfactory durability by avoiding the precedent breakage in a part of filaments in the cord having a multitwisted structure to suppress the lowering of the cord tenacity, and a tire having an excellent durability by using such a cord.

The steel cord having a multitwisted structure having a plurality of sheath strands each formed by twisting plural filaments around a core strand formed by twisting plural filaments is provided. At least one of the core strand and the sheath strands has a construction of twisting one or more sheath layers each made of plural filaments around a core made of one or plural filaments, and a diameter of a filament constituting an outermost sheath layer is made larger than that of a filament constituting at least one layer located inside thereof, whereby precedent breakage in a part of the filaments is avoided to suppress the lowering of the tenacity of the steel cord and improve the durability of the steel cord.