Magnetic nanocomposites with low coercivity and narrow hysteresis loop were prepared from amphiphilic polyurethane networks based on amphiphilic urethane acrylate precursor chains. The photoinduced curing or coalescence emulsion polymerization of amphiphilic polyurethane precursor chains produced two kinds polymeric matrices with different microstructure. Polymers prepared by coalescence emulsion polymerization showed a higher loading of FeCl3 and a greater magnetization value than the corresponding UV-cured networks.