The char-CO2 gasification reactions in molten blast furnace slag were studied kinetically by the isothermal thermogravimetry using STA409PC thermal analyzer. The effects of slag compositions (SiO2, MgO, CaO, and Al2O3) on gasification reaction were investigated. The results showed that CaO has certain catalytic effects on gasification reaction; however, when the gasification reaction temperature reached a certain value, the catalytic effect of CaO on gasification could be neglected. MgO also played a catalytic role in the gasification reaction. In this experiment, the gasification reaction rate increased with increasing the MgO content from 8 to 10 mass%, whereas it decreased with increasing the MgO content from 10 to 12 mass%. SiO2 had no catalytic effect on gasification reaction.