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The electrical conductivity of sintered pellets of nickel–nickel oxide mixtures of various compositions has been measured as a function of temperature in the range 700–1000 °C. The electrical conductivity of nickel oxide single crystals in air as well as in oxygen pressures corresponding to nickel–nickel oxide equilibrium has also been determined as a function of temperature. The conductivity of nickel–nickel oxide composites decreases initially, attains a minimum at approximately 1 mol % nickel and increases again with the increase in concentration of nickel. The activation energy for conduction remains constant for all compositions containing 20 mol % or less nickel. The variation of conductivity with compositions containing 1–20 mol % nickel is found to be in accordance with Wagner’s model. The decrease in conductivity of nickel oxide with the addition of 1 mol % nickel has been attributed to the trapping of holes from nickel oxide by electrons from the dispersed nickel.