The high-temperature fatigue crack growth (FCG) behavior at 400 and 500°C was investigated for variously heat-treated 17-4 PH stainless steels under different load ratios. Results indicated the FCG rates (FCGRs) at 400°C increased with R-ratio at the low ΔK regime and merged together at the high ΔK regime for all the given heat-treated conditions, except for a peak-aged condition. At 500°C, the FCGRs of the given alloys increased with R-ratio at low R-ratios and became comparable at high R-ratios. The variations of FCGR with R-ratio could be described as an intrinsic FCG behavior based on a Unified Approach. Accordingly, the predominant FCG mechanism was similar to a general plastic blunting process except for the high R-ratio regime of the peak-aged condition tested at 400°C.