More recently, ultra-high temperature ceramic composites (UHTCs) have received wide attention for a range of technological applications including aerospace applications, cutting tools, thermal protection structures, hypersonic vehicles, space shuttles and atmospheric reentry vehicles. TiB2-based composites are of particular interest due to the attractive mechanical and thermal properties and lower density (when compared to the other UHTCs). The addition of SiC in TiB2 matrix significantly improve the sinter-ability, strength and fracture toughness as well as high temperature oxidation resistance. Accordingly, TiB2-SiC composite are attractive for high-temperature structural applications. Nevertheless, it has some drawbacks such as arduous sintering process, weak thermal shock resistance and poor fracture toughness that challenge the use of these composite. The present work was designed and implemented to synthesis of TiB2/SiC composite by processes and study the effects of parameters (sintering temperature and holding time) and amounts of SiC, on the densification process and mechanical properties. Furthermore, carbon fiber was used as reinforcement to improve mechanical properties of these composite especially, fracture toughness, and effect of carbon fiber content on the mechanical and thermal properties of composite investigated. The powder mixtures of TiB2–SiC composites were ball-mixed to homogenize the powder mixture and then sintered via technique at temperatures of 1700-2000 °C for holding times of 3-10 min under a uniaxial load of 30 MPa. The study of parameters effects on the mechanical properties of TiB2-20 vol.% SiC composite revealed that the sample sintered at 1900 ? for holding times of 10 min under a pressure of 30 MPa exhibited maximum values of relative density (99%), micro-hardness (25 GPa), flexural strength (374 MPa), and fracture toughness (4.5 MPa.m1/2). Sinterability and mechanical properties of TiB2-based composites remarkably improved by addition of SiC compared to the monolithic TiB2. The TiB2–30 vol.% SiC showed an improved flexural strength of 400 MPa and indentation fracture toughness of 4.9 MPa.m1/2. Hardness measurements revealed an initial increase in hardness from 16 GPa for monolithic TiB2 to 25.5 GPa for TiB2-10 vol.% SiC and a subsequent decrease with further increase in the SiC addition. The Vickers hardness of TiB2-SiC composite decreased from 25 to 19.4 GPa when 15 %vol carbon fiber was included into the ceramic. Adding appropriate amount of carbon fiber led to increase fracture toughness and flexural strength however at higher reinforcement levels, the increase of residual thermal stresses, agglomeration and degradation of carbon fiber resulted in declining mechanical properties. The flexural strength of composites with 5 vol.% Cf reached the peak value (482 MPa), and composites with 10 vol.% Cf showed the highest fracture toughness of 6.7 MPa m1/2. Young's modulus of composite was decreased by addition of 15 vol.% Cf (by 50%) compared to the original TiB2–SiC composite. The coefficient of thermal expansion decreased with the increase of SiC content by 7%. The coefficient of thermal expansion of TiB2-30 vol.% SiC-(5, 10) vol.% Cf composite was higher than that of the original TiB2-30 vol.% SiC composite at temperatures between 50-500?. Inversely, the thermal expansion of TiB2-SiC-Cf composite was lower than that of TiB2-SiC at temperatures above 500?. Among all the fabricated composites, the sample reinforced with 15 vol.% carbon fiber reached the highest coefficient of thermal expansion (6.38×10-6 /?), compared with other prepared samples, which was due to the existence of graphitization transition layer between fiber and matrix.