Reactivities of a few raw coals and chars of these coals obtained from gasifiers operating under different conditions have been measured in C02 at temperatures of 840~1100 °C. The reactivities have been measured in a thermogravimetric analyzer up to complete conversions of the samples in most cases. Properties such as surface area, pore size distribution, porosity, and density have been determined for each sample. Actual pore structures of a few samples have been observed at different conversion levels by a scanning electron microscope. In order to compare the reactivities of different samples, the gasification process has been divided into two distinct stages: the first stage due to pyrolysis and the second stage due to char-C02 reaction. Reactivities due to the firs stage can be roughly related to volatile matter contents of the solids and the rate of heating. Through an Arrhenius type equation, an activation energy of about 2.5 kcal/mol is obtained for the first stage. The reactivity of a char in the second stage is found to depend more on its coal seam than on the gasification scheme in its production. Activation energy for the second stage reaction has been found to be about 59 kcal/mol. A rate equation has been proposed for the second stage that incorporates the effect of relative available pore surface area changing during reaction.