Abstract: Using cerium nitrate and ammonia as raw materials,cerium oxide nanoparticles were synthesized by single reverse microemulsion method in water/oil microemulsion system consisted of polyoxyethylene octyphenol(10)ether (OP-10)/normal butanol/cyclohexane/water solution.Samples were characterized by X-ray diffraction (XRD),thermogravimetric-differential scanning calorimetry (TG-DSC),transmission electron microscope (TEM),and ultraviolet-visible spectrophotometry (UV-VIS).TEM micrographs revealed that cyclohexane content in the system had great influence on the dispersion of cerium oxide nanoparticles;amount of substance ratio of water to OP-10 and reaction temperature had a significant impact on particle morphology of the product.Spherical and mono-dispersed cerium oxide nanoparticles with particle size of about 4 nm were successfully prepared when temperature was 25 ℃，mass ratio of cyclohexane was 60% in the total three organic components and amount of substance ratio of water to OP-10 was 15.The dispersion of nano-sized cerium oxide could be improved remarkably by using silane coupling agent A-1120 as a surface modification agent.UV-VIS showed that cerium oxide nanoparticles had excellent ultraviolet absorption capability.<BR>