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Highly dense AlN-SiC composites with various SiC additions (0-50 wt-%) were fabricated at 1800°C by plasma activated sintering. The effect of SiC addition on structural, thermal and dielectric properties as well as microwave absorbing performance of the composites was investigated. The thermal conductivity decreases with increasing SiC addition, from 68.7 W (m K) −1 for 0 wt-% SiC to 19.38 W (m K) −1 for 50 wt-% SiC. On the contrary, the permittivity and dielectric loss increase gradually, from 7.6-8.5 to 22-26.7 and from 0.02-0.1 to 0.2-0.53, respectively. AlN-SiC composite with better thermal and dielectric properties in 30 wt-% SiC, whose thermal conductivity and dielectric loss are found to be 24.88 W (m K) −1 and 0.15-0.74, respectively. Furthermore, the composite exhibits microwave absorbing performance with the minimum reflection loss (RL) of −16.5 dB at 15.5 GHz and the frequency range of 2.6 GHz for RL below −10 dB (90% absorption).