ABSTRACT In order to study the oxidation characteristics of anthracite at ambient temperature. Anthracite coal samples of three particle sizes were chosen for oxidation in a closed space at 25°C, thus the characteristics of O2 consumption and CO production during ambient temperature oxidation of anthracite were obtained for different particle sizes. The results showed that the O2 consumption rate and CO production rate of anthracite during the ambient temperature oxidation process were large at the beginning and then gradually decrease and finally reach equilibrium. The O2 consumption rate increases with increasing particle size in the range of 0.05–1.00 mm. In contrast, the rate of CO production exhibited a nonlinear pattern, which was highest for the medium-sized coal samples and lower for the largest and smallest samples. The ambient temperature oxidation experiment was repeated on the oxidized coal samples after rinsing with fresh air, during which CO can still be produced and the time needed for the reaction to reach equilibrium was shortened. In addition, the consumption of O2 and the production of CO were much lower than those of the first oxidation, and the influence of particle size on both the rates of oxygen consumption and CO production exhibited a nonlinear correlation. Comparing the results of the two experiments, the oxidation rate was fastest for coal samples with a particle size of 0.10–0.50 mm, while the oxidation rate of coal decreased when the particle size of coal samples was less than 0.10 mm. The research has some reference significance for fire prevention in anthracite coal mines.