Toegye's philosophy is identified as 'philosophy of Li' and 'philosophy of gyeong'. Toegye exhaustively entrenched philosophy of Li in Ontological and epistemological aspects and established philosophy of Gyeong which penetrates movement and serenity of a being and combines internal and external locus in a practical aspect of self-cultivation. The purpose of this study aims to analyze the theory of Geogyeonggungli(居敬窮理) and see how these Li and Gyeong are organically related and as a result, complete coherent philosophical system of Toegye philosophy. Toegye's philosophy is a self-causative and self-purposive study, that is, a self-cultivation to become a sage, wholly concentrated on 'becoming a sage'. Therefore, his theory on study strongly emphasizes on 'becoming a sage'. He believed that a sage is a person who embodied Seong(誠) and whose mind itself has become one with Li while its influence always retains relevant state by emitting human feeling appropriately. Toegye's Liqi theory((理氣論) and four-seven debate(四端七情論) had clarified the theory of Geogyeonggungli(居敬窮理) that is de facto a method to embody the theory. To accomplish such a state it necessitates, first, to study of Gungli(窮理) and second, to study of Geogyeong(居敬). The study of Gungli means developing a cognitive frame, which cognizes an external being as it is without distortion whereas the study of Geogyeong means cultivating body and mind, which prevents to distort the presentation of human nature. Ultimately throughout these two approaches, Li becomes an owner of its mind. Toegye insisted Geogyeong and Gungli are two different ways of becoming a sage in the meanwhile these two different approaches are heading towards one same direction, converging and integrating to become a sage.