Control of ferromagnetic colloidal properties has been demonstrated by variation of functionality and composition in the polymer surfactants used in the preparation of nanoparticles. The use of nitroxide mediated polymerization (NMP) afforded precise control of composition and functionality, yielding well-defined polymers that were subsequently used as surfactants in the preparation of ferromagnetic cobalt nanoparticles. Alteration of polymer molecular weight and composition allowed for systematic investigation of the effect of surfactant structure on magnetic colloid properties such as particle size and morphology. The stability of colloidal dispersions in various organic solvents was dramatically altered dependent upon the molar mass of the surfactant used in the preparation of the nanoparticles. In addition, the use of NMP allowed for the copolymerization of monomers with varying functionality to yield polymer surfactants for use in the preparation of functionalized magnetic nanoparticles.