The core-nanoshell composite materials doped with Sm were prepared by a solid-state reaction method. The core is magnetic fly-ash hollow cenosphere, and the shell is the nanosized ferrite doped with Sm. The thermal decomposition process of the sample was investigated by thermogravimetric analysis-differential scanning calorimetry ( TG- DSC ). The morphology and components of the composite materials were investigated by the X-ray diffraction analysis ( XRD ), scanning electron microscope ( SEM ) and energy disperse spectroscopy ( EDS ). The microwave absorption property was investigated by vector network analyzer ( VNA ). The results indicated that the exchange-coupling interaction happens between ferrite of magnetic fly-ash hollow cenosphere and nanosized ferrite coating. The exchange-coupling interaction enhances magnetic loss of composite materials. So, in the frequency between 1 MHz and 1 GHz, the absorbing effectiveness of the core-nanoshell composite absorbers can achieve –32 dB, it is better than single material and is consistent with requirements of the microwave absorbing material at the low-frequency absorption.