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In this work, C@Fe₃O₄ magnetic microspheres were designed and prepared by a novel strategy, and the microwave absorption properties of the materials were investigated. Four kinds of monodisperse P(MAA/St) microspheres with different carboxyl content were synthesized via facile dispersion polymerization. The Fe₃O₄ nanoparticles were grown on the surface of P(MAA/St) to obtain P(MAA/St)@Fe₃O₄ microspheres. Using P(MAA/St)@Fe₃O₄ as the precursors, after vacuum carbonization, C@Fe₃O₄ were obtained. It was observed that the carboxyl content on the microspheres’ surface increased with the increasing of MAA, which made the magnetic content and maximum specific saturation magnetization of P(MAA/St)@Fe₃O₄ and C@Fe₃O₄ increase. The obtained four kinds of C@Fe₃O₄ microspheres had a particle size range of 4−6 μm. The microwave absorption properties indicated that the magnetic content made a difference to the microwave absorption properties of C@Fe₃O₄ magnetic microspheres. The microwave absorption properties of materials were determined by controlling dielectric loss, magnetic loss and impedance matching. C@Fe₃O₄ microspheres exhibited excellent microwave absorption properties. The maximum reflection loss could reach −45.6 dB at 12.8 GHz with 3 mm in thickness. The effective bandwidth was 5.9 GHz with RL < −10 dB. Therefore, C@Fe₃O₄ microspheres were lightweight and efficient microwave absorption materials.