Ceria-based composites are developed and considered as potential electrolytes for intermediate temperature hybrid fuel cell applications (IT-HFC). The structural properties of composite materials based on mixtures of gadolinia-doped ceria (GDC) and alkali chloride (LiCl-KCl) are analysed. The microstructure of the electrolyte is observed by scanning electron microscopy (SEM). High temperature and room-temperature X-ray diffraction allowed determining the precise structure of the composite and its regular and reversible evolution with the temperature. Finally, the electrical conductivity is determined by impedance spectroscopy and presented as a function of the electrolyte composition. The ageing behaviour after thermal cycling and at a constant temperature of 400°C shows that this material is very promising. After such conditions, conductivity of GDC/Li-K-Cl composite electrolyte is still close to 0.12 S.cm−1 at 400°C, which is more than the Li-K carbonate/GDC composite conductivity at 600°C under the same conditions.