Monolithic SiC and SiC f/SiC composite materials have been fabricated by a reaction sintering process. The mechanical properties of RS-SiC f/SiC composites reinforced with Hi-Nicalon SiC fiber have been investigated at elevated temperatures, in conjunction with a detailed analysis of their microstructures. The effect of heat treatment on the microstructure and strength of RS-SiC material was also examined. The characterization of RS-SiC based materials was evaluated by means of SEM, EDS and three point bend test. The RS-SiC material showed an average density of 3.0 Mg/cm 3 and an average strength of about 550 MPa. However, the strength of RS-SiC material decreased with increasing heat treatment times. The RS-SiC f/SiC composite also experienced a reduction of room temperature strength at a test temperature of 1300 °C, owing to the creation of internal defects such as matrix oxidation, interfacial debonding and fiber degradation.