Physical properties of coal depend more or less on non-covalent bonding or on the resultant associated states of coal. Numerous investigations have so far been done to evaluate the states through observation of characteristics of solvent swelling and extraction of coal. In this experimental work, changes in mobility of hydrogen in coal at equilibrium swelling with mixed solvents of pyridine and CS_2 and its time variation were evaluated by means of ^1H-NMR and compared with those in volumetric swelling ratio. A close correspondence was found between them.