Abstract: Multi-wall carbon nanotube/Fe₃O₄ hybrids were prepared by a chemical synthesis-hydrothermal treatment method and their electromagnetic wave absorbing properties were investigated in the frequency range of 8.2-12.4 GHz (X band). As-prepared hybrids were characterized by transmission electron microscopy, X-ray diffraction and vibrating sample magnetometer. Results indicated that the surface of multi-wall carbon nanotubes was attached to magnetic Fe₃O₄ nanoparticles. The Fe₃O₄ content increased and the magnetism of the hybrids was enhanced by increasing the concentrations of Fe²⁺ and Fe³⁺ in solution. The minimum reflection loss (-18.22 dB, 12.05 GHz) was the lowest and the absorbing bandwidth was the widest when the concentrations of Fe²+ and Fe³⁺ were 0.02 and 0.04 mol/L, respectively.