Abstract : An investigation was carried out to characterize the effects of environment (including [NaCl] concentration) and load ratio on fatigue crack growth kinetics of HY-80 and HY-130 steels. Fracture mechanics wedge-opening-load (WOL) specimens oriented in the longitudinal direction (LT) were used in the current study. The test environments were vacuum, ambient air, and saltwater with [NaCl] concentrations ranging from 0.1 to 15%. Three load ratios, corresponding to R = 0.1, R = 0.5, and R = 0.85, were examined. The results indicate: (1) the fatigue crack growth rates and fatigue crack growth threshold, Kth, for HY-80 steel and HY-130 steel are comparable at similar stress ratios in each of the three test environments (vacuum, ambient air, and 1% NaCl solution); (2) in the low stress intensity region, the fatigue crack growth rates of both HY-80 steel and HY-130 steel are higher and Kth are lower at a high load ratio than those obtained at lower load ratios; (3) the fatigue crack growth rates of HY-80 steel and HY-130 steel obtained in ambient air and in 3.5% NaCl solution are comparable and are significantly higher than those obtained in vacuum; (4) the fatigue crack growth responses of HY-130 steel are not affected by the change in [NaCl] concentration; and (5) cathodic protection of HY-130 steel in saltwater does not lower its corrosion-fatigue cracking resistance.