Abstarct: Ceramic borides, carbides and nitrides are known for their high melting point, hardness, chemical neutrality, and relatively good oxidation resistance in unsuitable environments. This family of ceramics is called Ultra High Temperature Ceramics (UHTC). Some initial works were funded by the Air Force Materials Laboratory (AFML) in the early 1960s under a research program. These materials were tested to solve structural problems at high temperatures. This has led to the development of high-maneuverability supersonic fighters. In the meantime, NASA also conducted research on High Temperature materials to meet their needs. Many papers have addressed the relatively good oxidation resistance of diboride refractory compounds compared to other intermextallic refractory compounds. Hafnium diboride and zirconium diboride have been identified as the most suitable choices of the diboride transition mextals for high temperature applications such as missile warheads, sharp guiding edges, blades and similar objectives for use in supersonic fighters or their future generations. The current paper has used hafnium diboride for its unique properties compared to other materials. First, Hafnium diboride powder particles was ground with 80% (as weight percent) with 20% (as weight percent) silicon carbide in different grain sizes (microns, submicron, Nano) and in a separate sample by adding graphite with 2.5% and 5% (as weight percent) into a mixture of hafnium diboride and silicon carbide. Then, SPS process was sintered at 1900℃ at 40 MPa for 15 minutes. density tests, fuzzy identification, mechanical properties and oxidation resistance were investigated, following the sample preparation. the analysis presented in Chapter 4 indicates that grain size and graphite addition play an important role in the sintering behavior and relative density of the samples and also strongly affect the mechanical properties and oxidation behavior. Analysis shows that the relative density increased from 98.5 to 99.84 with finer grains, but with the addition of graphite up to 5% (as weight percent), the density decreased significantly. The presence of grain size in the structure increases the hardness from 19.04 GPa to 24.28 GPa. Also, the presence of graphite up to 5% (as weight percent) in the structure reduces the hardness by 75%. Although the presence of silicon carbide particles increases the oxidation improvement, but it was found that the grain size can be an effective parameter in improving the oxidation resistance.