Two chars prepared from parent coals of a high-volatile bituminous Coal and an anthracite coal were subjected to non-isothermal combustion tests in a thermogravimetric analyzer (TOA). The chars were burned in mixtures of O-2/CO2 and O-2/N-2 with O-2 concentrations of 3, 6, 10, 2 1, and 30%. A. range of nort-isothermal combustion tests of each char were conducted with linear heating rates of 2.5, 5, 7.5, 10, and 12.5 K/min. Detailed comparisons of measured char combustion rates show that replacing the inert nitrogen gas in the oxidizer with CO2 has very little influence oil the measured combustion rates of coal chars atanv char conversion level under the conditions of the experiments. Four different models free isoconversion methods using the experimental data were applied to determine the activation energies of the combustion of chars ill O-2/CO2 mixtures. The results show that the activation energy of each char, determined by any of the four methods, decreases with the increase of the char conversion level. The effect of diffusion, which becomes more pronounced at higher char conversion levels, is believed to be the main reason for the above observation, At a low char conversion level (e.g., 20%), when the effect of diffusion call be neglected, the activation energy of each char determined by the most accurate method under the conditions of this study was found to be in good agreement with literature data: for the anthracite char, it was 138.03 kJ/mol, and for the bituminous coal char, it was 127.83 kJ/mol. The measured combustion rate of each char was found to lie approximately first-order to the concentration of 02 ill the O-2/CO2 mixtures.