In this work, ZrB 2-SiC and novel C 3 N 4-doped ZrB 2-SiC composites were manufactured at 1850° C under an external load of 40 MPa for 6 min via spark plasma sintering. The effects of C 3 N 4 on the mechanical characteristics (flexural strength, Vickers hardness, and fracture toughness) and microstructure of the ZrB 2-SiC-based composites were investigated. By adding 5 wt% g-C 3 N 4 , a fully dense ceramic composite was fabricated, compared to the C 3 N 4-free ZrB 2-SiC composite with a relative density of 95%. Removal of ZrO 2 and B 2 O 3 from the surface of ZrB 2 particles via chemical reactions with C 3 N 4 , and the in-situ synthesis of ZrC and BN as new phases were studied by XRD and SEM analyses. Indentation fracture toughness, flexural strength, and Vickers hardness improved from 4.5 MPa.m 1/2 , 460.2 MPa and 17.4 GPa to 6.1 MPa.m 1/2 , 580.2 MPa and 21.2 GPa, respectively, by adding g-C 3 N 4 to the ZrB 2-SiC ceramic.