Utilization of the semi-coke collected from oil shale retorts is very important and advantageous. Due to the inflammable property, co-combustion of semi-coke with other good quality solid fuels could be effectual. In this research, a kinetic study of the combustion of oil shale semi-coke (SC) mixed with bituminous coal (C) was curried out by thermogravimetric analysis at different heating rates. Popescu's method was applied to analyze the kinetic mechanisms of combustion of oil shale semi-coke, bituminous coal and their blends: Flynn-Wall-Ozawa method was employed to determine the activation energies of those combustion reactions. Based on the obtained results, it was concluded that three-dimensional diffusion model could be implemented either for the combustion process of oil shale semi-coke or for bituminous coal while for their blends the model of random nucleation and growth could be applied. The activation energies of oil shale semi-coke and the blends of semi-coke and bituminous cool decreased in the beginning. and then increased during the combustion process. Activation energies of the blends decreased with increasing amount of bituminous coal.