Hollow glass microspheres/Fe3O4 (HGMs/Fe3O4) composites with low density were successfully synthesized by solvothermal method at 160 A degrees C. The morphology, composition, and microstructure of the samples were characterized by scanning electron microscopy and X-ray diffraction, respectively. The results show that the HGMs/Fe3O4 composites exhibit compact and continuous Fe3O4 particles coating on the surface of HGMs. The complex permeability and permittivity of HGMs/Fe3O4 composites obtained at 160 A degrees C for different reaction times were measured in the frequency range of 1-18 GHz by vector network analysis. The microwave absorption properties were well-elucidated by the traditional coaxial line method. The as-prepared HGMs/Fe3O4 composites show excellent microwave absorption properties. When the thicknesses of these HGMs/Fe3O4 composites are more than 1.5 mm, they all exhibit strong absorption peaks (lower than -10 dB). A possible mechanism of the improved microwave absorption properties was discussed.