Gelcasting was employed to fabricate Si₃N₄/SiC whisker (SiCw) composite ceramics. SEM showed the effects of heat-treatment temperature on the length-to-diameter ratio of the whiskers. The open porosity of composite ceramics declined and density increased as the whisker content raised when the sintering temperature increased. Study also showed that both the real (ε￠) and imaginary (ε2) permittivity of Si₃N₄/SiC whisker (SiCw) composite ceramics decreased with increasing frequency and increased as the whisker content raised in the frequency range of 8.2~12.4GHz. As the whisker content increased from 5 wt% to 15