We synthesized iron nanoparticles, 15–20 nm in size, having saturation magnetization, Ms, of 170 emu/g. They were embedded in copolymer beads of styrene (St) and glycidyl methacrylate (GMA), which were coated with poly-GMA by seed polymerization. The resultant Fe/St-GMA/GMA beads had diameters of 100–200 nm and Ms of 60 emu/g. By coating with poly-GMA, the zeta potential of the beads changed from -93.7 to -54.8 mV, as measured by an electrophoresis method. This facilitated (as revealed by gel electrophoresis method) nonspecific protein adsorption suppression, a requisite for nanoparticles to be applied to carriers for bioscreening.