The demand for microwave absorbing materials with strong absorption capability and wide absorption band is increasing due to serious electromagnetic interference issues and defense stealth technology needs. Here the carbon-coated Fe3O4 (Fe3O4@C) yolk-shell composites were successfully synthesized in a large scale for the application of microwave absorption through an in-situ reduction process from carbon-coated gamma-Fe3O4 precursor. The results show that the Fe3O4 nanoparticles are uniformly coated with a thin carbon layer about 10 nm in thickness and a clear void about 1 nm in width between Fe3O4 core and carbon shell are formed due to the volume shrinkage during the reduction treatment. The obtained yolk-shell composites exhibit excellent microwave absorption properties. The absorption bandwidth with RL values exceeding -10 dB is up to 5.4 GHz for the absorber with a thickness of 2.2 mm. The optimal RL can reach up to -45.8 dB at 10.6 GHz for the composite with a thickness of 3.0 mm. The outstanding microwave absorption properties may be attributed to the multiple interfacial polarization, good impedance match and multiple reflections and scattering owing to the unique yolk-shell structures. (C) 2017 Elsevier Inc. All rights reserved.