The reactivity of brown coal and upgraded brown coal (UBC), produced by coal-oil slurry dewatering process, for low-temperature oxidation was investigated in comparison with steaming coals using kinetic analysis of O-2 adsorption and weight variation during oxidation. The kinetic analysis was conducted by assuming first-order reactions of O-2 adsorption to form oxides and of decompositions of the original and oxidized components of the coal. The natural logarithm of each calculated rate constant (k) for three such reaction paths was found to be a linear function of reciprocal temperature. The rate constants Of O-2 adsorption obtained by different methods were plotted on the same line. These results indicate that low temperature oxidation process of the coals is expressed by such reaction scheme and rate constants. It is also recognized that O-2 adsorption is affected by the pore structure of coals, and the rates Of O-2 adsorption and pyrolysis of brown coal are much larger than those of the steaming coals at lower temperature. The slurry dewatering process was found to reduce the susceptibility to spontaneous heating of dried brown coal because the reactivity of UBC was smaller than that of the brown coal dried in vacuo.