The nano SiC(N) composite powder was synthesized from hexamethyldisilazane ((Me3Si)2NH) (Me:CH3) by a laser−induced gas-phase reaction. The microwave permittivity of the nano SiC(N) composite powder and paraffin wax (or other dielectric materials) composites can be tailored by the content of this nano powder. The dissipation factors (tgδ) of the nano SiC(N) composite powder are high at the microwave frequencies. And ε′, ε″ and tgδ of composites increase with the volume filling factor (v) of nano SiC(N) powder. The nano SiC(N) composite powder would be a good candidate for microwave absorbing material and electromagnetic interface (EMI) shielding material. The classical effective medium functions can not effectively model the microwave permittivities of the SiC(N) nanocomposites. We found that the microwave permittivities of the nanocomposites can be effectively modeled using second-order polynomials. These polynomials are dependent only on the filling factor and are purely mathematical models. The ε′ and ε″ of nanocomposites can be effectively modeled using second-order polynomials (ε′, ε″=Av2+Bv+C).