Hydrogen fluoride, boron trifluoride, and a mixture of them were examined as acid catalysts for solubilization of coal under milder reaction conditions. Hydrogen fluoride or boron trifluoride alone accelerated solubilization of subbituminous coal with toluene at 150 degrees C to some extent. Mixtures of hydrogen fluoride and boron trifluoride were found to solubilize coal considerably in the presence of toluene at 150 degrees C for 3 h under autogenous pressure of as low as 2.4 MPa without gaseous hydrogen. Coal solubilization depended on acidity in the reaction, reaction temperature and solvent. High extractability of the treated coal with HF/toluene depended on the cleavage of methylene, and the higher effectiveness of the HF/BF3/toluene system for the depolymerization of coal could be ascribed to more cleavage of ether groups as well as of methylene bridges.