The frequency dependences of the relative complex permeability mu(*)(r), the relative complex permittivity epsilon(*)(r) and the return loss for the composite made of sendust flakes or spherical sendust particles dispersed in polystyrene resin were investigated in the frequency range from 1 to 40 GHz. The values of epsilon(*)(r) increased when sendust flakes were dispersed in polystyrene resin and the frequency dependence of mu(*)(r) was different in the particles shape of sendust. Therefore, absorption characteristics depended on the particle shape of sendust and the absorption of electromagnetic waves with a wide bandwidth in the frequency range from 10 and 20 GHz could be achieved using spherical sendust particle with a low volume mixture ratio.