Oxidation properties of two coals, lignite and bituminous, at low and moderate temperatures were investigated using thermalgravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) methods. The apparent kinetic parameters were determined by the first-order Coats & Redfern method based on the TGA results. The mass developments of the two coals during the experimental temperature range of 25–400°C suggest that lignite is more prone to spontaneous combustion than bituminous coal. The kinetic analysis results show that all the absolute values of the apparent activation energies of lignite are less than that of bituminous coal, indicating that it is easier for lignite oxidation. FTIR spectra show that the structure of coals changed differently during oxidation. The aliphatic hydrogen groups (mainly the -CH₃ groups), associated hydroxyls, and substituent groups in aromatic structures decreased, and carbonyl species increased in bituminous coal. For lignite, both -CH₂ and -CH₃ groups decreased and carbonyls increase initially and then decrease corresponding to formation of a large amount of ether bonds. The substituent-aromatic structures increase slightly in lignite.