Seeded emulsifier-free emulsion polymerization was used to prepare poly(- styrene-co-acrylic acid) [P(St-co-AA)] microspheres. There are carboxyl groups on the surface of the P(St-co-AA) microspheres. Under appropriate conditions, the carboxyl react with NiCl2, etc., to form magnetic [P(St-co-AA)]Ni microspheres which exhibit ferromagnetic properties. ESCA analysis shows that the valence of nickel on the surface of the magnetic [P(St-co-AA)]Ni microspheres is 2. IR analysis confirmed that there are carboxylate groups present in the magnetic [P(St-co-AA)]Ni microspheres. Magnetic properties of this kind of polymer microspheres were studied. Results showed that the magnetic susceptibility decreased with decreases in temperature. The result of magnetic hysteresis loop studies showed that the obtained magnetic microspheres are categorized as magnetically soft materials. The coercive force (Hc) is 32 Oe, and the saturation magnetization is 1.79 emu/g.