The effects of carbon content, moulding pressure, and carbon particle size of green body on microstructure and properties of reaction-bonded silicon carbide (RBSC) have been investigated. The experimental results show that moulding pressure should match the carbon content of green body, or else, the properties of RBSC decrease. For the green body containing a certain size of SiC powders, the carbon particle should be less than a certain size, or else, the density and fracture strength of RBSC decrease with increasing carbon particle size.