Heat treatments of Zao Zhuang and Upper Freeport coals were carried out in several hydrogen-donating solvents at 175-300-degrees-C under N2 atmosphere. Retrogressive reaction of the coal, i.e., the decrease of carbon disulfide-N-methyl-2-pyrrolidinone mixed solvent soluble fraction, compared with that originally existed in the raw coal, was observed in tetralin even at temperature as low as 175-degrees-C, while in 9,10-dihydroanthracene or 1,4,5,8,9,10-hexahydroanthracene, which are much stronger hydrogen donors than tetralin, dissolution reactions, i.e., the increase of the mixed solvent soluble fraction, was observed at 175-300-degrees-C. The quantity of hydrogen transferred from the solvent to the coal was found to be well correlated with the extent of the dissolution reactions, and spin concentration in coal components decreased after the dissolution reactions, suggesting that the hydrogen donation to coal radicals from the solvent occurs during the heat treatment. The origin of the participating radicals, i.e., whether they are formed by the scission of weak covalent bonds or are indigenous radicals activated by heat, and the mechanisms of the retrogressive and dissolution reactions are discussed.