NiO/8YSZ (8 mol% Y2O3-stabilized ZrO2) composites with different NiO contents (10, 20 and 40 mol%) have been fabricated by a conventional route of mechanical mixing of NiO and 8YSZ powders and sintering at 1500 degrees C for 10 h in air. The resulting microstructures have been characterized by electron microscopy. In 10 and 20 mol% Ni0/8YSZ, the composite is formed by isolated NiO particles surrounded by zirconia matrix grains: this phase is interconnected in the 40 mol% Ni0/8YSZ composite. Mechanical tests at constant strain rate and at constant load were conducted on these materials at temperatures of up to 1350 degrees C. Different behaviors were found depending on the percolation of the NiO phase. Microstructural observations after deformation are essential to understand the overall mechanical behavior of the composites. (C) 2011 Elsevier B.V. All rights reserved.