In order to develop a reaction rate equation for the high concentration CO2, the regeneration reaction of CaCO3 was examined for the corresponding pressure condition in the temperature range 1123-1193 K. It was observed that the reaction rate was controlled by CO2 diffusion during the initial period and thereafter by the chemical reaction. In this study, the reaction rate equation was determined for the reaction-controlled period, which occupies the major part of the entire reaction. The reaction orders for the conversion process and pressure condition were obtained as 0.35 and 2.0, respectively. The reaction rate constant was also obtained, and the activation energy was estimated to be 102.68 kJ/mol.