Composite Electrolytes consisting of oxygen ion conductors and carbonates have received great attention for fuel cell application. The enhanced conduction was observed due to coionic(O=/H+) conduction during fuel cell operation under the H2/air atmosphere. It is believed that highly mobile ions at the interface between doped ceria and carbonates may contribute to the high conductivity of the composite electrolyte. Thus, the electrical conduction of composite electrolytes with various types of microstructures was evaluated at temperatures ranging from 300 °C to 700 °C. For powder mixture, the composite samples were prepared by direct mixing of doped ceria and carbonate powders. For infiltrated composite, the carbonates were infiltrated into porous ceria substrates at 600°C. SEM, XRD, and Electrochemical Impedance Spectroscopy were employed to conduct microstructural, structural and impedance analyses. The electrical conduction behavior of composite electrolytes will be rationalized based on the pore size, pore distribution and interface area.