Fe3O4 micro-spheres were synthesized by a simple chemical method at 90 degrees C. It was demonstrated that the final size and morphology of Fe3O4 was significantly affected by the additive NaF. The as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and vector network analysis. The complex permittivity and permeability of paraffin wax and Fe3O4 with different Fe3O4 volume fraction were measured to increase linearly with increasing volume fraction of Fe3O4 . When the matching thickness is 4 mm, the calculated reflection loss reaches a maximum value of -45.2 dB at 4.67 GHz with 40% volume fraction of Fe3O4 . (C) 2010 Elsevier B.V. All rights reserved.