The performance of nickel-based anode materials for solid oxide fuel cells (SOFCs) could be deteriorated by redox treatments accompanied with the microstructural change. In this study, Ni-yttria-stabilized zirconia (Ni-YSZ) anode was subjected to thermal cycles with redox treatments (thermal-redox cycles: repetition of oxidation in cooling and reduction in heating processes). The microstructural change of anodes was quantified by focused ion beam-scanning electron microscopy. The decrement in the active triple phase boundary (TPB) length caused by sintering and agglomeration of Ni particles was correlated with the performance deterioration. Furthermore, it was found that the onset temperature of reduction treatment in the heating process was one of the critical factors for the microstructural evolution of anode; the agglomeration of Ni particles was promoted significantly under the reduction started from 500 degrees C, while no notable change was confirmed for the case of 900 degrees C. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: [email protected]. All rights reserved.