We discuss a facile approach to control the size and the magnetic properties of CoFe2O4 nanoparticles by varying the solvent dielectric constant. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Thermo-Gravimetric Analysis (TGA) and Vibrating Sample Magnetometer (VSM) are used to study the structural, thermal and magnetic properties of CoFe2O4 nanoparticles. XRD analysis confirms the cubic spinel phase of CoFe2O4 nanoparticles. The average particle size increases from 10 +/- 1 to 16 +/- 1 nm as the dielectric constant of the solvent is increased from 47 to 80. The room temperature magnetization measurement confirms that the saturation magnetization increases with particle size. The linear dependence of the dielectric constant of the medium on particle size is in good agreement with nucleation theory. Our experimental findings unambiguously confirm that the change in supersaturation has a significant influence on the nucleation rate and the particle size. (C) 2009 Elsevier B.V. All rights reserved.