With the continuing growth in demand for the reduction of electromagnetic radiation, lightweight and highly efficient microwave absorbents are greatly needed. In this study, Fe₃O₄@C core–shell nanotubes, with Fe₃O₄ nanotubes as cores and carbon as shells, of about 10 nm thickness have been successfully synthesized. Coating Fe₃O₄ nanotubes with carbon shells effectively increased dielectric loss and improved impedance matching of the composites, resulting in enhanced microwave absorption performance. The effective absorption bandwidth, with reflection loss (RL) less than −10 dB, was up to 6 GHz when the thickness of the test sample was as little as 1.7 mm, as determined using a vector network analyzer. Possessing a very low density of 1.4 g cm⁻³ and good microwave absorption performance, the as-fabricated Fe₃O₄@C core–shell nanotubes can meet the multiple property requirements of microwave absorbents.