We have recently presented a method that converts low-rank coal into upgraded coal and thermoplastic extract through the hydrothermal degradative extraction in a flow of hot water at less than 350 degrees C. To examine the validity of the presented method and to characterize the upgraded coals and the thermoplastic extracts obtained in more detail, seven kinds of low-rank coals, a biomass, an O-methylated brown coal, an oil rock, and a bituminous coal were subjected to the hydrothermal degradative extraction at either 300 or 350 C. The elemental compositions of the upgraded coals were found to be rather close to each other, and their carbon and oxygen contents were larger than 71% and less than 23%, respectively, meaning that the heating values are well over 30 MJ/kg on a dry ash-free (daf) sample basis. The solid extracts (deposits) obtained at 350 degrees C from the variety of samples were very close to each other in elemental composition, molecular-weight distributions, pyrolysis behavior, and softening/melting behavior. All of the deposits interestingly completely melted without decomposition below 200 degrees C. Thus, the proposed method was found to be effective to convert low-grade carbonaceous resources into solid fuel having a higher heating value and compounds having thermoplastic property under rather mild conditions.