Abstract: The polystyrene beads were grafted with poly(acrylic acid) chains through photo emulsion polymerization, forming the spherical polyelectrolyte brushes (SPB). Magnetic nanoparticles (MNP) were generated in nanoreactors of SPB by co precipitation reaction. The contents of MNP were also increased by multiple loading reactions. SPB immobilized with MNP (SPBM) were studied by Small Angle X-ray Scattering (SAXS). As loading reaction time increased, the content of MNP in SPB was increased and the size distributions became more uneven. The position where maximum concentration of MNP lay depended on both the concentration of ferric and ferrous ions and the spatial resistance.