Nano-sized Si/C/N powders are prepared from hexamethyldisilazane ((CH3)(3)Si)(2)NH) by chemical vapor deposition (CVD) at different pyrolysis temperatures from 900 degrees C to 1200 degrees C. The as-formed Si/C/N nano powder is amorphous, and after controlled heat-treatment, SiC crystals formed. The composition of the Si/C/N powders prepared at different conditions is analyzed and the result shows that the nitrogen content of the Si/C/N powder is related to the synthesizing temperature. Si/C/N powders heat-treated at different temperatures are mixed with paraffin wax and the microwave permittivity of the mixture is measured. The result shows that the epsilon ', epsilon '', and the dissipation factor tg delta (epsilon ''/epsilon ') of the mixture are high at the frequency of 8.2 similar to 12.4GHz, and the nitrogen content and the degree of crystallization have influence on the microwave permittivity. We believe that the high value of epsilon ', epsilon '' and tg delta are due to the dielectric relaxation as the result of nitrogen atoms doped in silicon carbide lattice.