Hydrogen exchange reactions of coal with tritiated water and gaseous hydrogen were investigated to estimate the mobility of hydrogen in coal using not only a batch type reactor but also a flow type reactor. Specifically, the reactivities of functional groups were traced in these reactions. In the reaction of coal with tritiated water at 100 degreesC the hydrogen exchange of functional groups such as hydroxyl group in coals could be estimated. In the pressurized system using stainless batch type reactor aromatic hydrogen at ortho- and para-positions of a functional group could also be estimated by the hydrogen exchange reactions of coal and tritiated water at higher temperature. In hydrogen exchange reactions of coals with tritiated gaseous hydrogen using a flow reactor, reaction temperature was controlled exactly. The use of a Pt/Al2O3 catalyst promoted the generation of hydrogen radicals which reacted with coal. This method enables us to estimate the reactivity of a functional group with a hydrogen radical. Further, it was found that the particle size of coal only slightly affected hydrogen exchange ratio of coal in both cases of tritiated gaseous hydrogen and tritiated water.