To characterize chemical structure of oxidized coal, solid state 13C MAS NMR spectra were acquired for bituminous coal with lower water contained (=low moisture) and with higher water contained (=high moisture) before and after estimation of their self-heating property using R70 apparatus. It was found that low moisture coal reached 80°C in shorter time than high moisture one. The chemical structural change in low moisture coal during oxidation was found to be increasing aldehyde, ketone and carbonyl, while that in high moisture one was found to be decreasing aldehyde and ketone. It is suggested that the dominant chemical reaction which induces self-heating of coal depends on the amount of water contained in coal before oxidation.
