This experimental work deals with the influence of niobium additions to high purity nickel on dynamic recrystallization behavior during hot working. Various high-purity alloys were prepared (unalloyed Ni and Ni–0.01, 0.1, 1 and 10 wt % Nb) and deformed to high strains by hot torsion tests to characterize the rheological behavior within the range 800 – 1000°C at strain rates of 0.03, 0.1 and 0.3 s–1. Niobium additions strongly increased the flow stress. To quantify such behavior, the strain-hardening parameter h and dynamic-recovery parameter r in the Yoshie-Laasraoui-Jonas constitutive equation were determined from the initial part of the experimental stress-strain curves (i.e., at strains before the stress peak) in which dynamic recrystallization does not alter the mechanical behavior. A table showing the variation of h and r as a function of strain rate, temperature, and niobium content was compiled and used to fit a simple empirical model for predicting h and r from the deformation conditions and alloy composition. In addition, microstructures were determined by optical metallography and SEM/EBSD. Based on this work, it appears that niobium additions noticeably refine the steady-state grain size by considerably decreasing the kinetics of dynamic recrystallization in nickel.