In this paper, the mechanical properties, especially fatigue crack propagation behaviors of a newly developed Ni-base superalloy Allvac ® 718Plus™ Alloy were investigated, as compared with those of Alloy 718 and Waspaloy. It is indicated that 718Plus TM alloy shows better performance on tensile, creep and fatigue crack growth tests than Alloy 718 at room temperature, 650°C and 704°C. In the final section of the paper, the mechanism of fatigue crack propagation behavior of superalloys and hold-time effect are discussed. Examination of the fatigue fracture surfaces by scanning electronic microscope (SEM) revealed transgranular crack propagation with striations for 718Plus TM at room temperature. There is a clear border between the fracture surface of the room temperature pre-crack and 0.33Hz fatigue at 650 C. The fracture mode at 650 C is the mixture of intergranular and transgranular modes. When the test temperature is up to 704 C, intergranular is the predominant mode and the whole surface covered by a layer of oxide film, indicating that severe oxidation happens during the crack growth. The crack path of 718Plus TM under 3+100 seconds' hold-time conditions at 650°C and 704°C are predominantly intergranular, with a little transgranular cleavage fraction. The fracture was rough and covered by lots of oxide products. These oxides are believed to be from oxidation asperities of -phase precipitates.Fatigue crack growth of most superalloys is predominantly a cycle-dependent damage process with little frequency effect at very high frequencies. At relatively low frequencies or the test with hold-time, crack growth includes time dependent processes, which were generally ascribed to phenomena involving creep and/or environmental degradation processes. The combined mechanical and SEM fractographical analysis show the timedependent FCG of 718Plus TM is rather an environmental effect than creep effect.