We describe here the synthesis of a novel magnetic drug-targeting carrier characterized by a core-shell structure. The core-shell carrier combines the advantages of a magnetic core and the stimuli-responsive property of the thermosensitive biodegradable polymer shell (e.g., an on-off mechanism responsive to external temperature change). The composite nanoparticles are similar to 8 nm in diameter with similar to 3 nm shell. The lower critical solution temperature (LCST) is similar to 38 degrees C as determined by UV-vis absorption spectroscopy. The carrier is composed of cross-linked dextran grafted with a poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) [dextran-g-poly(NIPAAm-co-DMAAm)] shell and superparamagnetic Fe3O4 core. Fourier transform infrared spectroscopy (FTIR) confirmed the composition of the carrier. The synthesized magnetic carrier system has potential applications in magnetic drug-targeting delivery and magnetic resonance imaging.