For the binary system of ${alpha}$-SiC and graphite the optimized condition of stable dispersion was investigated by controlling surface charge and dispersant in the previous work and then the preforms and sintered boy were fabricated. In this work the effects of stable dispersion on the microstructure and mechanical properties were investigated for reaction bonded silicon carbide. It was shown that reaction bonded silicon carbide had a uniform and homogeneous microstructure and the newly formed ${eta}$-SiC was obsdrved around the original ${alpha}$-SiC For the mechanism of reaction bonding process firstly the carbon particles were dissovd in liquid silicon and then precipitates out around original ${alpha}$-SiC and it grew epitaxially. For this reaction bonded silicon carbide having homeogeneous microstructure the mechanical properties such as bending strength fracture tough-ness weibull modulus were characterized. Also crack propagation mode was investigated through analyzing fracture surface. The density of reaction bonded silicon carbide was 2 . 9g/cm3 4-p. bending strength was in the range of 310${pm}$20 MPa. and the fracture toughness was 3.0 MPam1/2 The crack propagated with intergranular and transgranular mode