The hydrogen transfer behavior of five different ranks of coals on their reaction with the tritium-labeled toluene or tetralin in the temperature range from 200 to 400 degreesC for 5-360 min has been investigated. The behavior of hydrogen in functional groups was also traced. The extensive hydrogen transfer to coal occurred with tetralin even at 300 degreesC, while only a small amount of hydrogen was transferred from toluene. The hydrogen exchange of functional groups occurred with tetralin, although it was difficult for hydrogen exchange to take place with toluene. The transfer of hydrogen/tritium from the tritiated tetralin to the coals occurred not only by the conversion of tetralin into naphthalene but also by hydrogen exchange. This showed that although tetralin can readily be dehydrogenated to the aromatic, the tetralyl radicals formed by the reaction with coal radicals are also reactive as hydrogen acceptors. On the other hand, some structural elements existing in the coals should be good hydrogen donors, which transfer hydrogen to the tetralyl radicals. The enhancement of hydrogen transfer reactions occurred with the lower rank Illinois No. 6, Wandoan, and Beulah-Zap coals, compared to the higher rank Upper Freeport and Pocahontas No. 3 coals because of the existence of a relatively large amount of thermally labile or sensitive oxygen functional groups in these coals.