Abstract: The SiC_W/Si₃N₄ composite ceramics were prepared by gel-casting using α-Si₃N₄ powder and β-SiC_W as the raw materials and Al₂O₃ and Y₂O₃ as the sintering aids at 1 650℃ and kept 1.5 h. The effects of the content variation of SiC_W on the microstructure, mechanical and room/high temperature microwave absorbing properties of the SiC_W/Si₃N₄ composite ceramics were investigated. The results show that the flexural strength and fracture toughness of the SiC_W/Si₃N₄ composite ceramics have a trend of decrease after an initial increase with increasing SiC_W content. It possesses the most excellent flexural strength and fracture toughness (505 MPa and 9.515 MPa·m^1/2) when the content is 10wt%. The real part of the dielectric constant at room temperature reaches the maximum 12 with the 10wt% SiC_W. The maximum absorption is -21 dB at 12 GHz. And the high temperature permittivity has a trend of decrease after an initial increase with increasing SiC_W content. The real permittivity reaches 12.5 when the content is 10wt%. Compared with the pure Si₃N₄ ceramic, when the SiC_W content is 10wt%, the lowest reflectivity of the SiC_W/Si₃N₄ composite ceramic reduces to -27 dB at around 11.7 GHz, and the effective absorption band (less than -5 dB) ranges from 11.2 to 12.3 GHz.