This study treats State Succession of the Boundary convention between the North Korea & China(1962) after the "Unified Korea" regarding the Gando Convention between Japan-China in 1909. The Gando convention is legally based on the 1905 Japan-Korea Protectorate Treaty. This treaty(1905) has never been ratified by Korea Emperor Gojong. Furthermore, the Japanese officials used military coercion against Korean cabinet members to forcibly conclude the treaty. This 1905 Japan-Korea protectorate treaty is null and void. So the Gando convention is also null and void. Therefore, China's territorial sovereignty over the Gando has no legal title at all. In the perspective of international law, the Gando territorial dispute still remains unresolved. This study focuses on the relationship between positive international law and the territorial issue of Gando after the "Unified Korea". Despite that the Vienna Convention on Succession of States in Respect of Treaties has been concluded in 1978 and has become effective since in 1996, only few states remain as the members of the treaty. The 1978 treaty is not a general international law. Furthermore, China, South Korea and North Korea did not sign this treaty. It is said that the 1978 treaty would be a kind of codification of state practice, but there were, in the meantime, many state practices inconsistent with the treaty. In case of state succession issues, the successor state continuously creates new state practices through concluding new conventions with the concerned states. So, state practices are very inconsistent. And analyses of state practices show that the state succession to treaty varies according to two types of changes: the change of the territorial sovereignty and the change in patterns of treaties which directly relate to the state succession. In the case of the border treaties, which are dispositive treaties, successor state tends to prevail regardless of the type of the change in the territorial sovereignty. Article 11 of the 1978 Vienna Convention provides for the principle of continuity for a boundary established by a treaty. However, this principle should not be applied simply to all the boundary conventions. Article 11 of the Boundary Convention on succession of States in Respect of Treaties(1978) should not be applied to the 1962 and 1964 agreements between China and North Korea. Herein, special historical charters regarding the Korean division and the Japanese colonial times should be taken into consideration. Article 12 of German unification treaty does not accept the principle of automatic succession regarding treaties of predecessor state(East Germany). In conclusion, article 11 of the 1978 convention (the principle of continuity) should not be applied automatically to the boundary treaty in 1962 and the boundary protocol in 1964 between North Korea and China. They will be disputed by the Unified Korea regarding state succession in the future. The case of article 12 of German unification treaty would be a good example in resolving this problem. Therefore, regarding the boundary treaties of North Korea and China, intensive consultations between the "Unified Korea" and China shall precede before reaching to a conclusion on this matter.