Low-temperature oxidation of coal was attempted to be applied to the evaluation of the amount of mobile hydrogen which might locate at active methylene sites such as methylene carbons in a position a to aromatic rings. In-situ FT-IR measurement during oxygen treatment clearly indicated that the decrease of methylene groups and the increase of carbonyl groups including carboxyl groups occurred even at a temperature as low as 120 degreesC. The increment of carbonyl groups, which was monitored using FT-IR analysis, was compared with the weight increase during oxidation under the same conditions. These two sets of data were well correlated so that the weight increase determined by thermogravimetry was applied to the evaluation of the amount of mobile hydrogen-in other words, transferable hydrogen-with the assumption that chemical reactions take place during the oxidation treatment. The results were compared with the values estimated by other methods.