A differential thermal analyzer (DTA) and a X-ray diffractometer (XRD) were used to study the solid transformations in binary SnO2-CeO2 oxide system. For 100wt% Sn and 100wt%Ce, the transformations from amorphous xerogels to rutile and fluorite start from about 310 and 250°C, respectively. The crystallizations to two-phase mixtures of rutile and fluorite take place at higher temperatures. The two-phase mixtures appear in the region whose composition is between about Sn-10wt%Ce and Sn-75wt%Ce. Sintered at 450°C for one hour, rutile phase dissolves about 10wt% fluorite, and fluorite dissolves about 25wt% rutile. Precipitation reactions take place when the sintering temperature is raised. The phenomenon that precipitation reactions are observed for rutile and fluorite solid solutions means that lower temperature sintering produces solid solutions with high supersaturation. In the as-sintered samples, the grain sizes are fine nano-crystals and the complicated microstructures help the other cations to locate at discontinuous regions.