SiC has great potential to be used as high temperature electromagnetic wave absorbing material. However, its absorbing performance is still low mainly due to the poor conduction loss caused by the intrinsic low electric conductivity. So the increase in electric conductivity can effectively increase its absorbing performance. In this paper, aluminum doped SiC whiskers were synthesized by microwave heating. Thus the carrier concentration can be effectively increased as confirmed by Raman spectra. And a 3D network of conductive path for the dissipative current can be formed through whiskers connecting. In this way, the conduction loss was increased significantly through the enhanced electrical conductivity. Both the dielectric loss and microwave absorption of SiC whiskers increase with the increase in dopant concentration further confirmed they are conductivity dependent. When the Al/Si ratio is 0.03/0.97, the lowest reflection loss is achieved at −25.4 dB and the effective absorption bandwidth is 2 GHz.