The all-ceria-composite ITSOFCs have demonstrated extraordinary fuel cell performances since the ceria-composite electrodes are very catalytic and conductive, and the ceria-composite electrolytes are highly conductive and also electrolytic, in addition to excellent compatibility between the electrolyte and electrodes based on the same ceria-based composite materials. The power density outputs from 200 to 800 mWcm-2, were obtained for temperatures between 400 and 700°C. The maximum power density 0.72 Wcm-2 (1500 mAcm-2) at 600°C and 0.82 Wcm-2 (1800 mAcm-2) at 700°C were achieved, respectively. These highly catalytic electrodes functioned extensively for many different fuels, such as hydrogen and hydrocarbon fuels, e.g., natural gas, coal gas, methanol and ethanol etc. In some special cases, the ITSOFCs with the ceria-composite electrodes could also work at as low as 200°C. All these good performances are based on the novel catalyst function of the ceria-composite electrodes and internal reforming mechanism.