TOEGYE(退係)(LEE HWANG;李滉), a great philosopher and educator of Josun Dynasty, lived in the mid-16th century. As he grew in the good environment, studied philosophy very hard, perceived the Principle of the Cosmos and the Nature. The philosophy of TOEGYE is called SUNGRIHAK(性理學), so he explained that the Cosmos is made up of IKIIWONLON(理氣二元論) based on LI(理) and KI(氣). LI, the origin of the creatures, is the same with SUNG(性), the origin of the Cosmos. Above all, human beings made much of GYUNG(敬) which cultivated his spirit. After he was 50 years personality, he emphasized that we, human beings, had to observe propriety and morality, love his children, be dutiful to his parents. Husband and wife had to respect each other. Especially, they maintained the harmony of their homes. His Educational Thought is, first of all, to set human`s steady purpose in life, to perform his personality, to respect individual character, to render aid to the poor in charity, to get rid of the excessive greediness, to be economical, and to love the nature. He used a method of the Conversation or a method of the Question and Answer to teach his pupils. However, In case of having no answer, he corresponded with his pupils to catch question. We have to follow Toegye`s Educational Thought based on the cultivation of the Personality, a steady will, the performance of Morality and Propriety(孝) and his economical spirit, he was dedicated to the education of the young.