Kinetics of solid state reaction and grain growth behavior of BaTiO₃-CaTiO₃-SrTiO₃ system ceramics has been studied. It is shown that the formations of both BaTiO₃ and SrTiO₃ are due to the phase boundary controlled reaction. On the other hand, that of CaTiO₃ is diffusion controlled. Grain growth of this system could be expressed by the equation Gⁿ=kt, where n=8.0 and Q=690kJ/mol (activation energy) were obtained under Po₂=10^-10Pa. It is possible to control the microstructure of this system by oxygen partial pressure(Po₂) during firing. When Po₂≤10_-8Pa, the microstructure of this system becomes fine and uniform.