Nickel oxide/zirconia composites with different NiO contensts have been fabricated by mechanical mixing of nickel oxide and zirconia powders and sintering at 1500 ºC for 10 h in air. The resulting microstructures have been characterized by scanning and transmission electron microscopy. The mechanical behaviour of the composites has been characterized by compressive tests at high temperatures between 1100 and 1350 ºC. For NiO contents above the percolation limit, the softer phase was found to be rate-controlling in oxidizing atmospheres, achieving extended steady states of deformation without macroscopic failure. By contrast, the overall creep strength of the composites decreased severely in reducing conditions.