CO2-gasification reactivity of unburned carbon in both coarse and fine slags was studied in a pressurized thermogravimetric analyzer (TGA) and compared with a char obtained from a drop tube furnace (DTF) at 1400 degrees C from the same original coal. Results show that the reactivity of the unburned carbon in the coarse slag is always higher than that in the fine slag, around 1.11 to 1.88 times. The DTF char is less reactive than the unburned carbon in both fine and coarse slags. In order to understand the effects of minerals on the CO2-gasification of unburned carbon, reactivity of the unburned carbon in demineralized slag was also investigated. Results show that the minerals in the coarse slag catalyze the CO2-gasification of unburned carbon, but that in the fine slag inhibit the CO2-gasification. An elemental analyzer was adopted to analyze C, H, N and S in the original coal, the DTF char and the slags. The main reasons for the differences in the gasification reactivity of unburned carbon in the slags are the morphology of slags, the degree of graphitization of unburned carbon and the components of crystalline phase, which have been investigated by SEM/EDX and XRD. It is found that a higher ordering of carbon layers and a lower content of catalytic components are the main reasons for the lower reactivity of the unburned carbon in the fine slag compared to that in the coarse slag. (C) 2009 Elsevier B.V. All rights reserved.