The electrode kinetic behavior of nickel was studied by potentiokinetic, potentiostatic, and potential decay techniques in sulfate solutions of pH 1.3, 3.4, and 6.3 adjusted to constant 0.1N ionic strength by K2SO4 additions. The active-passive transition characteristic of the room temperature behavior of nickel was found to be absent at temperatures above 100°C. However, at temperatures above 250°C, indications of oxide formation were found although there was little contribution to passivity therefrom. In addition, the temperature stability of passive films and these oxides seems to be pH dependent. Theoretical potential-pH diagrams were also constructed for the nickel-water systems for the temperature range used in these experiments.