The role of temperature and load ratio on the crack propagation rate of Alloys 276 and 617 under cyclic loading was investigated. The results indicate that the rate of cracking was gradually enhanced with increasing temperature when the value was kept constant. However, the temperature effect was more pronounced at . Both alloys exhibited maximum values at a load range of 4.5 kN that corresponds to an value of 0.1. The number of cycles to failure for Alloy 276 was relatively higher compared with that of Alloy 617, indicating its slower crack-growth rate. Fractographic evaluation of the broken specimen surface revealed combined fatigue and ductile failures.