An attempt has been made to quantitatively investigate the effect of microstructural changes on gasification reactivity of coal chars. Pocahontas No. 3, Illinois No. 6, and Beulah-Zap coal char samples were gasified in 1% O-2 at 500 degreesC or 600 degreesC up to 90% (daf) conversion, and their structure were observed under a high-resolution transmission electron microscope (HRTEM). A quantitative structural analysis was done based on HRTEM images to obtain structural parameters such as number of stacks, layer size diameter, and their distributions using an image analysis algorithm. Effect of mineral matter on structural changes was also studied by carrying out gasification experiments with demineralized chars. The gasification reactivity of these chars was correlated with the structural parameters.