This paper studied structures of ceria-carbonate two-phase composites, with an emphasis on the interfacial structures and interactions between the two constituent phases of ceria and carbonate. The phase structure was analyzed by DSC, XRD and SEM. The IR measurements were carried out to identify the bonding situations and interfaces. Some new absorptions and wavenumber shifts of the bands appeared in IR spectra. There are strong indications of the interfacial phenomena exist in the two-phase composites through comparison between the two-phase composite with each individual constituent phases. The results opened a new interesting subject on the two-phase composite structures with significant importance for applications in advanced low temperature (300-600°C) SOFC.