A new creep constitutive equation for Ni-base superalloys under high temperature-low stress condition was proposed previously. This creep curve had good reproducibility of the creep behavior under the condition of 1100°C/137 MPa. In this paper, an improvement of this creep constitutive equation is reported; in particular, to achieve better regression at the early secondary creep stage with a logarithmic function. The refined creep constitutive equation was fitted to the same creep curves that had been with the previous equation and an improved regression was obtained. The new creep curve gives very good estimations especially for creep ratios of all creep stages. The result of multi regression with composition for an additional parameter, due to the improvement, is also reported.