In the premodern East Asian world, “ritual protocols(‘禮’),” particularly the ones that were usually observed between King and the vassals[君臣], were also observed between countries and dynasties, which did not have equal footing but instead had different statuses, as ‘superior and subordinate’ countries. In this article, examples and cases of such King-Vassal protocols being observed and practiced in the Goryeo-Khitan diplomatic relationship during the reign of Goryeo king Hyeonjong are searched for, presented and examined. Of course, how such practices reflected the condition of the time is examined as well. Unlike the relationship that existed between Joseon and Ming, in which all rituals and protocols were not only considered as mere ‘protocols’ (detailed and quite visible) but also construed as a demonstration of ‘principles’ shared by all parties, in Goryeo-Khitan relationship, the Goryeo government observed and practiced these king/vassal protocols in quite a visible and outward fashion in order to find a way to coexist with a superior dynasty that was Khitan Liao. Focus of examination in this article was placed upon the fact that the Khitan government, which was trying to find the right time and the right reason for invading Goryeo, cited no other than the insurrection of Gang Jo, which could be labelled as an act that blatantly deviated from (the spirit of) protocols[‘非禮’], and then initiated a decade of warfare. It was particularly interesting that such blatant disregard of the way of things that had been only culminated in a final invasion that was ended with Goryeo achieving a huge victory and led to the restoration of a previous relationship, which ensured both past and present peace between the two countries based upon a traditional tributary/appointment relationship.