Low rank coals are abundantly deposited and widely distributed, although they have not been used on a large scale except at the mining sites because of their high water content and oxygen content, and because of the high possibility of self-ignition when dewatered. Therefore, treatment for both dewatering low rank coals and suppressing their self-ignition tendency as well as increasing their heating value is essential. In this study, the possibility of the degradative solvent treatment, which treats coals in a non-polar solvent at 350℃, was examined as the method for self-ignition suppression, and the factors influencing self-ignition tendency was discussed.