Ferromagnetic Fe3O4 nanoparticles were synthesized and then self-assembled into microparticles via a solvothermal method, using FeCI3.6H2O as the iron source, sodium oleate as the surfactant, and ethylene glycol as the reducing agent and solvent. The obtained Fe3O4 microparticles were characterized by X-ray powder diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, Raman spectroscopy and vibrating sample magnetometer （VSM）. The size and morphology of the particles were examined using transmis- sion electron microscopy （TEM） and scanning electron microscopy （SEM）. The Fe3O4 microparticles of nearly monodisperse diameters, controllable in the range of 120-400 nm, consist of assemblies of Fe3O4 nanoparticles with a diameter of 22 nm. The effects of reaction time, amount of surfactant and NaAc on the products were discussed. Interestingly, by using the pre-synthesized Fe3O4 microparticles as the growth substrates, spherical and smooth-looking Fe3O4 microparticles with average diameter of 1μm were obtained. A plausible formation process was discussed.
