Fe3O4 nanoparticles coated by oleate were prepared by means of coprecipitation method. The influence of temperature, concentration, stirring speed and feeding method on particle′s size was studied. Then the particles were coated with dextran for the second layer, and coupled with polypeptide to apply in Magnetic Resonance Imaging(MRI). The results showed that the particles
obtained under stirring speed of 7 000 r/min, temperature of 70 ℃ and FeCl2 concentration of 01 mol/L were about 8 nm in size and
superparamagetic with singledomain crystal structure. The composite Fe3O4 particles can specifically gather in the tumor with the concentration
of 213 times of physiological saline.