We have proposed and developed a new creep constitutive equation for Ni-base superalloys. In this paper, an application of the creep constitutive equation for long time creep test is discussed. Several creep curves of the test conditions of 1000°C/137 MPa and 900°C/245 MPa are fitted and achieved a good reproducibility. It is also examined to predict the rupture time of a continuing long time creep test from the behavior of the initial stage creep. The initial part of the creep data is fitted by the creep constitutive equation to extract initial creep stage parameters, and parameters belongs to the later creep stage are got by multi regression analysis.