The kinetics of the reaction of Ca(OH)2 with CO2 in humid N2 has been studied at 60−90 °C by using a differential reactor. Ca(OH)2 reacted with CO2 to form CaCO3 only when the relative humidity exceeded 0.08. The reaction ceased before 1 h, and Ca(OH)2 was incompletely converted. The reaction rate and final conversion of Ca(OH)2 were significantly affected by relative humidity, were slightly dependent on temperature, and were zeroth order with respect to gas phase CO2 concentration. The carbonation of Ca(OH)2 was well described by the asymptotic equation which is obtained by assuming chemical reaction control and considering the surface coverage by product. The rate-controlling step might be the dissolution of Ca(OH)2 at the water-adsorbed surface. The reaction behavior of Ca(OH)2 with CO2 was similar to that with SO2. The model derived for the reaction with CO2 may be applied to that with SO2 with proper modifications. The results of this study are useful to the design and efficient operation of the processes using hydrated lime to remove SO2 from the flue gas, in which both SO2 and CO2 are present.