Glycidyl-functionalized poly(N-isopropylacrylamide) was synthesized via RAFT. It was used for controlling degree of nanoclustering of magnetite nanoparticle (MNP). The cluster (20–150 nm) had good water dispersibility and magnetic responsiveness. It showed thermo-responsive behavior at temperature above its LCST (34 °C). It might be used in controlled release works with temperature-triggering mechanism.