Abstract: CeO2 nanoparticles were prepared using cerium nitrate and hexamethylenetetramine as starting materials, and the prepared powders were collocated into polishing slurry for chemical mechanical polishing of GaAs wafer. Various size of nanoparticles had the different polishing effect, of which the 8 nm particles exhibited the best polishing effect with the lowest surface roughness 0. 740 nm, and those smaller or bigger than such size got higher surface roughness. By taking simplified solid-solid contact models into consideration, the chemical polishing manner played a dominant role and resulted the worse surface performance because it is difficult for abrasives to penetrate into the soft layer if the particles were too small. On the contrary, when the particles were larger than certain size, the surface roughness increased because the depth which particles embeded into martrix increased. The best polishing can be obtained while the depth of particles indented into wafer surface was equal to or near to the thickness of soft layer.