AlN-SiC Composites were obtained by hot-pressing at 1900ı for 1h in a nitrogen atmosphere. The influences of the amount of SiC on densification behavior and microwave attenuation characteristics were studied. The results showed that although the densification of composites decreased along with the increasing SiC content, it had no distinct influence on microwave attenuation characteristics. When the content of SiC increased, the attenuation of AlN-SiC composites increased within the range of 2 to 8 GHz. SiC is a kind of wide frequency attenuation agent.