Polymerization process for preparing monodispersal organic/inorganic composite nano-microsphere in the field of nanometer technology is disclosed. The process comprises preparing two different miniemulsion systems of A with inorganic nanoparticles and B with polymerisable monomers in advance; adding water-soluble initiator into A, stirring till complete dissolution, then adding B to stir till mixing evenly;finally, heating the mixed system to a given temperature for isothermal reaction. The grain size of the superparamagnetic Fe 3 O 4 /polystyrene is homogeneous and controllable, and the magnetic particles content is controllable.