The fatigue crack growth (FCG) rates of mill annealed Alloy 60 in 0.1M NaCl soluton, 25℃, were studied by a fracture mechanics test method. They were affected by the applied potential, load frequency and load ratio. At an applied cathodic potential of -1300mV (subscript SCE), the FCG rates increased with lowering the load frequency and with increasing the load ratio. The enhanced FCG rate was found in the lower load frequencies (≤0.1Hz) and was more significant with increasing the load ratio. The load ratio effects were successfully accounted for employment of the Walker model. The secondary cracks and transgranular fracture modes were observed on the fractured surfaces with applied cathodic potential. The possible hydrogen-assisted cracking mechanism on enhancing the FCG rates of Alloy 600 cathodically charged in 0.1M NaCl solution, 25℃, was discussed in this paper.