Carbon- and silicon carbide (SiC)-based materials, especially in the form of composites, have attracted more attention from reactor technologists than have other ceramics because they better fulfill the prime requirements of reactor materials, such as high-temperature stability and low susceptibility to irradiation and nonbrittle fracture. These composites are fabricated through different routes and may vary in their properties. Therefore, sufficient data need to be generated on the microstructure and mechanical properties of these composites. In the studies reported here, carbon- and SiC-based fibrous ceramic composites were prepared using a liquid-infiltration sol-gel technique with carbon fibers as reinforcement and hybrid sol and pitch as matrix precursors. To some compositions, SiC nanoparticles were added. The composites were heated to 1000°C and 1500°C. The sol-gel route results in an amorphous mixed oxycarbide, silica, and carbon matrix, which on heat treatment at 1500°C is converted to a semicrystalline SiC matrix composite. Scanning electron microscope examination of carbon fiber/carbon and carbon fiber/SiC composites showed good wetting of fibers by matrix resin, forming good bonding at the interface. The carbon fiber/SiC composites with SiC nanoparticles as additional reinforcement showed higher density as well as a 34% increase in flexural strength compared with those without nanoparticles. The addition of just 1 wt% of SiC nanoparticles decreased oxidation by 4 wt%.