The core–shell Ni/SnO2 composites were synthesized through a facile hydrothermal method using Ni microspheres as cores, SnCl2 as stannum source, and H2O2 as the oxidizing agent. The microwave absorption properties of Ni microspheres and Ni/SnO2 composites were investigated at 1.018.0GHz. It was shown that the reflection loss (RL) of Ni/SnO2 paraffin-composite can be evidently enhanced compared with Ni microspheres paraffin-composite, and the minimum value is −18.6dB at 14.7GHz. The enhancement mechanism was discussed based on complex relative permittivity (ε r =ε'−jε″) and relative permeability (µ r =µ'−jµ″). [ABSTRACT FROM AUTHOR]