ABSTRACT Since the preliminary data suggest that Fe-25Ni-20Cr austenitic stainless steel (Alloy 709) is an excellent candidate as a structural material for high-temperature applications such as Sodium-cooled Fast Reactor (SFR), the effect of strain range on creep-fatigue interaction of the Alloy 709 is investigated by conducting strain-controlled creep-fatigue tests with tensile hold times of 0, 600, 1,800 and 3,600 s at strain ranges varying from 0.6% to 1.2% at 750°C and 2 × 10−3 s−1 strain rate. Strain-controlled fatigue tests were performed at strain ranges from 0.3% to 2.5% at 750°C and 2 × 10−3 s−1 strain rate. The predicted fatigue life of Alloy 709 shows a better correlation with the characteristic slopes predictive method. With increasing strain range at a given hold time, the number of failure cycles decreases until saturation. The fractography of the deformed samples exhibited increased number of cracks with strain range along with M23C6 precipitates and high dislocation density.