Nickel-gadolinium doped ceria (Ni-GDC) composite anodes gain a lot of attention as they have potential to be a beneficial solution for the intermediate temperature solid oxide fuel cells. In this paper, the influence of the initial microstructure of Ni-GDC anode on the polarization characteristics and its deterioration in 100h operation are investigated. The initial microstructures of the investigated anodes are determined by the different sizes and aspect ratios of the GDC powders, but all anodes having the same initial compositions of NiO: GDC = 60:40 vol.%. It was found that the anode with the smallest GDC particle had the best initial performance, but also underwent the most severe degradation. Themicrostructures of the fabricated anodes were investigated by focused ion beam-scanning electron microscopy (FIB-SEM), and microstructural parameters were quantified to relate the electrochemical performance. From the experimentation, contribution of the Ni-GDC microstructure to the anode polarization characteristics is discussed. The morphological evolution after the operation is also in discussion, especially those of the GDC phase. It was concluded that the mobility of GDC could be an influential factor determining the change in polarization resistance. (C) 2019 The Electrochemical Society.