Cobalt ferrite nanoparticles of different sizes are prepared by varying the concentration of Co²⁺ metal ions using precipitation approach. The average crystallite size, coercivity (H_C), and saturation magnetization (M_S) increases from 11 to 16 nm. 0 12 to 0.8 kOe. and 28 to 52 emu/g, respectively, as Co²⁺ ion concentration is reduced from 0 4 to 0.025 M High resolution transmission electron microscopy and X-ray diffraction analysis confirms that CoFe₂O₄ nanoparticles are ciystalline in nature with cubic structure. Raman spectroscopic investigation shows traces of paramagnetic ferrihydrate in samples prepared with Co2+ ion concentration greater than 0 1 M These experimental results suggest that metal ion concentration plays an important role in the size, magnetic property and purity of precipitated cobalt ferrite nanoparticles. The variation in the average crystalline size with Co²⁺ ion concentration is in good agreement with the nucleation theory. Our approach is useful in tuning the size and magnetic properties of cobalt ferrite nanoparticles