Hydrogen transfer reactions of coal with tritiated gaseous hydrogen in the presence of tetralin were performed using a flow reactor under the following conditions: pressure 50 kg/cm2, temperature 200−400 °C, and reaction time 120−420 min. When Wandoan coal (WA) was used as a coal sample, functional groups participated in the hydrogen transfer reaction even at 200 °C and then decomposed at 250 °C. At 300 °C, ether bonds were cleaved to generate hydroxy groups which were decomposed at 350 °C. When the higher rank Pocahontas coal (POC) was used, functional groups participated in the hydrogen transfer reaction even at 250 °C and then decomposed at 300 °C. Further, ether bonds were cleaved at 350 °C to generate hydroxy groups which were decomposed at 400 °C. These results showed that in the case of POC coal, a 50 °C higher temperature was needed to obtain functional group behavior similar to the case of WA coal.