CeO₂ nanosheets were directly synthesized by a precipitation process with the aid of 1-butyl-3-methyl-imidazolium ionic liquids at room temperature. The anion species and the concentration of the room temperature ionic liquids (RTILs) have a great influence on the morphology of the resulting products. The as-prepared CeO₂ is irregular and agglomerated seriously in the absence of RTILs, while it changes from nanocube to nanosheet with increasing the RTIL concentration or decreasing the polarity and hydrophilicity in the orders [Bmim]Cl > [Bmim]Br > [Bmim]BF₄ > [Bmim]PF₆. The CeO₂ nanocubes have relatively uniform grain size distribution with size of 4.5–6.4 nm, and the nanosheets are assembled by a great deal of nanocrystalline whose length and width extend to hundreds of nanometers. The as-synthesized CeO₂ exhibits an excellent removal capacity for the organic pollutant Congo red dye, indicating its potential use in practical wastewater treatment.