On 26th March 2010, It is the day when 20th anniversary of Korean-Mongolian diplomatic relations. Historically and Culturally between Korean and Mongolian have had a deeply relationship. Especially in Koroy Dynasty, between Koroy Dynasty and World Empire Won Dynasty had a strongly alliance like a brother. So Koroy Dynasty had made a special history to communicate and to cooperate a worldwide. After then, in Joseon Dynasty, Korean Peninsula had cut to cooperate with Mongolia because of a small-chinaism. And since modern ages the relationship of Korean Peninsula and Mongolia have developed to create a new history. Of course after World-War Ⅱ that relationships were begun by South korea and North korea. That's why the study on diplomatical cooperation of korean Peninsula and mongolia has been separated. The relationship of North korea and Mongolia was started in 1930s. At that time North korean and Mongolian fought against the Japan-Imperialism as called 'Hallingol battle'. And in Korean-War Mongolia had served to the North korea. That's why North korea and Mongolia had become a strong alliance. But since 1990 when South korea and Mongolia had a diplomatic relations, The relationship of North korea and Mongolia needs to change for the new future.