The dielectric properties of high-temperature stable singlesource precursor-derived SiC/HfCxN1-x/C ceramic nanocomposites are determined by microwave absorption in the X-band (8.2-12.4 GHz) at room temperature. The samples synthesized at 1700 degrees C, denoted as SiC/5HfC(x)N(1-x)/C-1700 degrees C and SiC/15HfC(x)N(1-x)/C-1700 degrees C ceramics, comprising approximate to 1.3 and approximate to 4.2 vol% HfCxN1-x, respectively, show enhanced microwave absorption capability superior to hafnium-free SiC/C-1700 degrees C. The minimum reflection loss of SiC/5HfC(x)N(1-x)/C-1700 degrees C and SiC/15HfC(x)N(1-x)/C-1700 degrees C are -47 and -32 dB, and the effective absorption bandwidth amount to 3.1 and 3.6 GHz, respectively. Segregated carbon, including graphitic carbon homogeneously dispersed in the SiC matrix and less ordered carbon deposited as a thin film on HfCxN1-x nanoparticles, accounts for the unique dielectric behavior of the SiC/HfCxN1-x/C ceramics. Due to their large reflection loss and their high chemical and temperature stability, SiC/5HfC(x)N(1-x)/C-1700 degrees C and SiC/15HfC(x)N(1-x)/C-1700 degrees C ceramics are promising candidate materials for electromagnetic interference applications in harsh environment.