The present study concerns oxygen-ion transfer between yttria-stabilized zirconia (YSZ) single crystals under mechanical contact stress. Two YSZ single crystal plates were piled up between platinum meshes, and contact stress was mechanically applied. The interfacial conductivity as well as the bulk conductivity was successfully measured with this setup. The interfacial conductivity is greatly influenced by the contact stress, whereas the bulk conductivity is almost independent of the stress. The interfacial conductivity is significantly increased with increasing contact stress, especially from 0 to 5 MPa, and is saturated around 56 k Omega cm(2) with the stress around 40 MPa. The interfacial capacitance increases with contact stress. The activation energy for the interface conductivity is equal to 105-111 kJ/mol, similar to that for the bulk, and appears to change slightly with stress. (C) 2013 Elsevier Ltd. All rights reserved.