Industrially,many kind of metal oxide nanoparticles are synthesized for various purpose.[1] Cerium oxide is also one of them.Since size and morphology of nanoparticles have an great effect on physical and chemical properties of nanoparticle,various synthesis processes to control particle size and morphology have been studied.[2] Among those studies,synthesis with organic modifier process is very successful technology.Cerium oxide nanoparticles can be also synthesized with organic modifier such as decanoic acid.[3] However,when cerium oxide is synthesized,it is obtained as colloid suspension in organic solvent.If cerium oxide is stored in organic solvent,various problems are occurred such as transportation difficulty,storage difficulty,particle aggregation,volatile solvent,and fire.To overcome these problems,it is necessary to store cerium oxide nanoparticles as dried solid..Conventionally,hot air drying is easily used as drying process of metal oxides.Although this process can be carried out simply,capillary force between liquid-vapor interface has damage on nano-structure.To avoid this problem,freeze drying process is suggested.However,long drying period is still problem like hot air drying.Since washing of residual organic material is also essential before these drying processes,generation of excess organic solvent is inevitable.In this study,however,aerosol solvent extraction system(ASES) with supercritical CO2 is suggested as another drying process without washing process.It is competitive with its advantages like less particle aggregation,less waste water,and less process time compared to conventional drying process.Dried cerium oxide nanoparticles are analyzed by FT-IR,XRD,and HR-TEM.With these analyses,it is confirmed that cerium oxide is completely dried without residual organic material.In perspective of this study,it is thought that drying of other metal oxides by ASES using supercritical CO2 is also attractive process.