We study the effect of divalent metal hydroxide solubility product on the size and magnetic properties of nanoparticles formed during co-precipitation. We synthesized ferrite nanoparticles by varying the solubility product from 10 −13 to 10 −17 by using different divalent cations of Mn, Co, Fe and Zn, where the average particle size decreased from 29.1 to 8.9 nm. The Mn, Co and Fe ferrites were magnetic in nature with saturation magnetization of 44.6, 47.38 and 56.19 emu/g respectively, whereas the Zn ferrite was paramagnetic. The increase in particle size observed with increasing solubility product of divalent metal hydroxide is in agreement with the nucleation theory.