In this work, the BaF2 nanopowders with different particle size were synthesized by precipitation in the ethanol/water mixed solvents. Five kinds of compositions of mixed solvents, including pure water, 25 vol.%, 50 vol.%, 67.5 vol.%, and 75 vol.% of ethanol were used. The effects of aging and the volume percentage of ethanol in the mixed solvents on the resultant BaF2 nanoparticles were under investigation. The size and morphology of the BaF2 particles were characterized by TEM, FSEM and XRD analyses. The results show that after aging for 2 h the particle size of the BaF2 precipitates in the 50% mixed suspension changes little. The prepared BaF2 particles all exhibit cubic fluorite structures no matter what kind of composition is used. In pure water environment, the size of BaF2 particles is about 70 nm, whereas it reduces to 33 nm in the 75% mixed solution. As the vol.% of ethanol increases the particle size decreases, and other properties such as the size distribution, dispersion, oriented growth et al. are also modulated. These alterations can be interpreted by varying the dielectric constant of mixed solvent. (c) 2007 Published by Elsevier B.V.