We prepared the magnetic nanoparticles of Fe3O4from thermal decomposition of the Fe oleates precursors synthesized by iron chlorides and sodium oleate,and the SiO2-coated Fe3O4nanoparticles by combining the reverse microemulsion and organic template methods. FTIR was adopted to investigate the surface of Fe oleate under different treatments,and the growth of Fe3O4 nanoparticles with different reactant concentrations of oleic acid and heating rates. The results indicated that the superficial oleic acid of the waxy solid Fe oleates after extraction from ethanol and acetone was partially removed,which impairs the formation of monodispersion Fe3O4 naoparticles. The effect of heating rate on the growth of nanoparticles was weak compared with that of the concentration of Fe oleates. When the concentration of oleic acid is 0.09 mol/L, a characteristic peak of Fe3O4 at 576 cm-1(assignable to the bending vibrations of Fe-O) is enhanced significantly. The XRD (X-ray diffraction) spectra,TEM (transmission electron microscopy) images and SQUID (superconducting quantum interference device) confirmed that the Fe3O4 nanoparticles are spinel cubic crystal and have a good monodispersity and super-paramagnetism. Whats more,the TEM of SiO2-coated Fe3O4 nanoparticles also confirmed that the Fe3O4 nanoparticles were well coated by mesoporous SiO2.