In general,inorganic filler/polyurethane elas-tomer (PUE) composites possess favorable properties,such as modulus,chemical resistance,and heat stability,are promising for broadening the application area of poly-urethanes (PU).For the experiments,a series of cerium oxide (CeO2)/PUE composites were prepared with differ-ent sizes and appearance of CeO2,and different mixing methods as well.CeO2 particles with different sizes were added into PUs during the formation of urethane linkage and the chain-extend process,respectively.The morphol-ogy along with mechanical properties,thermal properties of the composites were studied.The results suggest that the size of CeO2 and mixing methods influence the microstructure of PUs which has profound effect on properties of these composites.The composites tend to form more quantity of hard domains (HDs) with small size when CeO2 particles were added before the formation of urethane linkage,whereas CeO2 particles increase the size of HDs when added with chain extender into PU prepolymer.