Polycrystalline NiO samples were equilibrated with different oxygen partial pressures from 10-3 to 1 Atm in the temperature range 750 °C -1000 °C. Transient electrical conductivity was measured until a new equilibrium was attained after changing the oxygen partial pressure. By the time dependence of the electrical conductivity in isothermal conditions the diffusion coefficient of nickel vacancies was determined. Using the pertinent value for the vacancies equilibrium concentration, the self-diffusion coefficient of nickel in nickel oxide was obtained in good agreement with literature data.