In this paper, the fatigue strength and the fatigue crack propagation behaviors of the round bar specimens which were spirally built up by welding and subsequently hardened by quenching were investigated. The material used was SF60 which was whdely employed in mechanical components, especially shafts. Fatigue tests were conducted at the fully reversed condition(R=-1) and axial and load control in the room temperature ahd air environment. The experimental results were expressed by both the range of stress intensity factor ($Delta{K}$) and the effective range of stress intensity factor ($Delta{K}_{eff}$). It was clarified that applying of quenching after the building up welding process improved the fatigue strength and the gatigue crack propagation property in the low range of $Delta{K}$ of the built up round bar specimen.