The reactions between silicon nitride and carbon take place in two stages, the surface silica of silicon nitride powders reacts with carbon first followed by the decomposition of silicon nitride and the residual silicon reacting with carbon. The kinetics of the two stage reactions has been studied by isothermal thermogravimetric analysis. Physico-geometric models for both of the reaction stages have been proposed, and the kinetic parameters have been calculated. The implications of the kinetic models and parameters are discussed.