In situ electron paramagnetic resonance (EPR) spectroscopy was used to investigate the behavior of free radicals in a lignite Banko coal (%C: 71.3%) that was heated to 300 degreesC at a rate of 10 degreesC/min in a hydrogen-donating solvent 1,4,5,8,9,10-hexahydroanthrancene (HHA), a polar solvent N-methyl-2-pyrrolidinone (NMP), and mixtures of the two solvents (NMP/HHA). With HHA, the radical intensity increased slightly as temperature increased from 60 to 200 degreesC, and then decreased greatly as it increased to 300 degreesC, due to the stabilization of radicals by hydrogen transferred from HHA. In contrast, the radical intensity in NMP increased greatly from 60 degreesC to 260 degreesC and then decreased slightly. NMP, an aprotic polar solvent, might interact with the free radicals and prevent the radical molecules from recombining and taking part in addition reactions. When NMP/HHA mixtures were used, changes in the radical intensity was dependent on the proportion of HHA. Moreover, the EPR spectra were deconvoluted to narrow and broad lines, and the behavior of the broad-line components was found to be related to coal dissolution in HHA.