TMCP steel manufactured by controlled rolling followed by accelerated cooling process is known to have extra-ordinary mechanical properties such as tensile strength and toughness. However, there is much uncertainty about the fatigue fracture characteristics, especially, in the welded state of this steel. In case of this steel, the softening zone by welding is generated in heat affected zone in contrast with the case of conventional normalized high strength steel. This softening zone is considered to play significant roles in low cycle fatigue fracture of the welded part of this steel. In this paper, the low cycle fatigue behaviors of TMCP steel were inspected in as-received and welded state using the smooth specimen. The fatigue life-time was seperately investigated on the basis of failure of the specimen and crack initiation which is detected by differential strain method. Moreover, the low cycle fatigue characteristics of TMCP steel were quantitatively compared with those of the conventional normalized steel of same strength level.