The effect of coal ash on the electrochemical performance of solid oxide electrolyte-based carbon fuel cells (SO-CFCs) is investigated in this study. The polarization and durability performance of SO-CFCs fueled by lignite char, ash-free char, and ash-added char were measured and compared from 1023 to 1123 K The influence of five different coal ashes and six typical inorganic species was evaluated in SO-CFCs during short-term operation. The anode morphologies were analyzed to clarify the cell degradation. The results indicate that lignite char shows a higher initial cell performance but a lower stability than ash-free char in SO-CFC. The higher initial cell performance is attributed to the superior CO2 gasification reactivity, while the lower stability is more likely caused by carbon and ash deposits. The effect of coal ash on the cell performance is strongly dependent upon the ash composition. Inorganic Ca, K, and Fe species in coal ash improve the initial cell performance by catalyzing char-CO2 gasification reactivity. Inorganic S and Fe species in coal ash tend to react with anode Ni particles and form large aggregations on the anode surface, leading to anode deactivation. In combination with inorganic Ca, Fe, and K, Si and AI compounds in ash could form irregular-shape deposits on the anode surface and clog up the anode pores. The ash with a high content of SiO2 and Al2O3 (93.39 wt % in total) shows no adverse effect on the cell performance. This study suggests that proper coal ash pretreatment should be conducted to improve the cell stability of coal-fueled SO-CFCs.