This study aimed at preparation of B 4 C-SiC nano composites and also characterization and comparing with pure one. In first step, sinterability of boron carbide and mechanical properties of it were studied and also the influence of adding silicon carbide nanoparticles that were synthesized in this study as well as graphite to B 4 C matrix was investigated. In this regard spark plasma sintering () was used. The results showed fullu dense boron carbide sintered at 1700 ?C for 3 min as optimal conditions. However, with the highest hardness resulting from lower values of the average grain size, fracture toughness did not improve considerabley. The fracture toughness is greatly improved in composites compare to the pure boron carbide specimens and the improvement is more notable in composite without graphite. Improvement in the fracture toughness of composites can be attributed to activating of toughening mechanisms from the influence of SiC nanoparticles distributed in B 4 C matrix on the crack path. The addition of SiC particles as a second phase to B 4 C matrix also has strong influence in fracture surface. For fully dense pure boron carbide almost all of the grains fractured transgranularly. However, in nanocomposites that sintered at same condition the B 4 C matrix fractured transgranularly whereas intergranular fracture occurred at the interfaces between SiC grains and B 4 C grains. Silicon carbide nanoparticles, as a reinforcement, synthesized by carbothermic reduction of silica in furnace and later in microwave. Results showed SiC nanoparticles were produced in furnace at 1450 ?C for 60min and in microwave at 1200 ?C for 5 min. Finally for the first time high temperature deformation of boron carbide and B 4 C-SiC nanocomposite were presented. Plastic deformation is admitted to be produced by dislocation activity and grain boundary sliding. The presence of solute atoms seems to play a crucial role on the main creep characteristics in this material. On the other hand, the presence of an increasing cavitation is consistent with limited grain boundary sliding. Keywords : SiC, B 4 C, Microwave processing, Spark plasma sintering, Mechanical properties. * Professor, Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran. ** Associate Professor, Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.