The thermal behavior and kinetic parameters of decomposition reaction of limestone in a temperature-programmed mode were investigated by means of TG. The experimental results show that the kinetic model functions in different forms for the thermal decomposition reactions of different limestone grain sizes in dispersing state under the atmosphere of static air are 4(1-α)3/4 for small size limestone and (1-α) for large size limestone. Information was obtained on the relationship among the decomposition temperature, decomposition time, decomposition fraction, decomposition reaction rate constant and grain size of limestone.