Spark plasma sintering (SPS) process was used to preparation of ZrB2-based composites co-reinforced with SiC whiskers as well as various amounts of pulverized carbon fibers. The effects of C-F content on microstructure and mechanical characteristics of ZrB2-SiCw-C-F composites were scrutinized. Although all composites approached high densification, a fully-dense sample was fabricated by the addition of 2.5 wt% C-F. The growth of ZrB2 grains was remarkably inhibited in C-F-reinforced composites. No in-situ formed phase was detected by XRD; however, trace of nano-ZrC clusters was observed in SEM fractographs of ZrB2-SiCw-C-F samples. The formation of such nano-sized ZrC refractory phase was also proved by thermodynamics. The hardness of composites slightly decreased from 21.9 to 19 GPa with increasing the C-F content. Reversely, the fracture toughness values enhanced from 4.7 to 6 MPa.m(1/2) with increasing the amount of pulverized carbon fibers.