8 mol% yttria-stabilised zirconia (8YSZ) was annealed at high temperature under various compressive stress conditions. The conductivity was measured during the annealing whilst the grain structure as well as the crystal structure was examined before and after annealing. The conductivity of 8YSZ subjected to no stress decreased with the annealing time due to the increase of the tetragonal phase. The compressive stress of 50 MPa had no effect on either the decrease of the conductivity or the increase of the tetragonal phase. The compressive stresses of 100 and 200 MPa had also no influence on them, except for the initial decrease in the conductivity caused by the fracture. The average grain size was almost constant regardless of the annealing time, temperature and the compressive stress. The degradation phenomenon of 8YSZ therefore could not be influenced by a compressive stress of up to 200 MPa. (C) 2012 Elsevier B.V. All rights reserved.