Co-SiC core-shell powders were prepared by electroless plating. Scanning electron microscopy (SEM) revealed that Co-SiC core-shell powders were of nearly sphere-like shape and were about 0.3 μm. X-ray powder diffraction (XRD)patterns showed that the cobalt powder was hexagonal crystallite. The complex dielectric constant and the complex permeability of Co-SiC core-shell powders-paraffin wax composite were measured by the rectangle waveguide method. It showed that the dielectric loss was less than 0.1 and the magnetic loss was about 0.2 in 8.2-12.4 GHz for prepared Co-SiC core-shell composite powders.