In this paper, the HRTEM technique has been applied to the structural study of Pt-Rh catalysts supported on Ce doped SiC. The results on cerium doped active carbon and on cerium doped silicon carbide synthezised before its use as catalyst support are also reported. It was found that the Ce doped SiC catalyst support contains a new compound which is a Ce amorphous phase. The presence of such a compound within the support is thought to have the advantage of contributing to the improvement of the activity of the catalysts, At present, the HRTEM study on reduced Pt-Rh/SiC-Ce catalyst gives direct evidence of a selective association of Pt and Ph metals with the cerium oxide additive. This association, on the one hand, shows that cerium oxide is not inert towards noble metals, and on the other hand, it gives rise to a noble metal-cerium oxide composite to which the reduction is linked. The formation of an active interface, or a buffer oxygen layer which can be defined as a surface that serves as a common boundary between noble metals and cerium oxide, must be then considered in order to interpret the improvement in catalytic activities. After the ageing treatment, some structural changes were observed, particularly the formation a Rh suboxide phase formed by three to four monoatomic layers. Finally, it seems that the main oxidation and reduction processes occur through the active interface where the cerium oxide is easily able to change from cerium plus four (Ce4+) to cerium plus three (Ce3+) oxidation state. The metal, will act only as a donor or acceptor of electrons. It must be emphasised that the SiC catalyst support showed a high chemical inertia since no structural modifications were observed on the noble metals caused by SiC.