HyperCoal (HPC) is an ashless coal produced by thermal solvent extraction from a coal and is expected to be useful for several utilization technologies because of it is mineral matter free and high softening property. Although HPC can be produced from various ranks, HPC extraction yield from low-rank coals is low due to the influence of hydrogen bonds among functional groups. Extraction yield can be increased by using a polar solvent for breaking the hydrogen bonds leading to increased yield. In this study, the relationship between the extraction yield by a polar solvent and oxygen functional groups was investigated. The results showed that the effectiveness of polar solvent increased with increasing phenolic hydroxyl content and an excellent correlation between the effectiveness of polar solvent and the phenolic hydroxyl content in coals was found.