The legitimacy of the Nine-Dash line of the 2009 China Declaration in the South China Sea

China issued a map to the UN Secretary-General announced the drawing of a Nine Dash Line in the South China Sea, In 2009. This Nine-Dash Line cover's all the main islands of the South China Sea. Also, the method of delimitation with this Nine-Dash Line is such that it interferes with the Exclusive Economic Zones and the Continental Shelf of other neighbors. This way of drawing lines was not reformed even with China's accession to the Convention on the Law of the Sea (1982). The Philippines as the most affected and protesting country, Claims incompatibility of China's Nine-Dash Line with the United Nations Convention on the Law of the Sea (1982) and considered all Chinese actions contrary to its obligations under this convention. According to this Convention and aimed at resolving disputes, The Philippines submitted its bill and petition to the Arbitral Tribunal pursuant to Annex 7 of the Convention. The summary conclusion of this study is that although the delimitation of borders, including maritime borders, is unilaterally practical in principle, a country cannot introduce itself as a coastal country outside the scope of international law and in areas that overlap with other coastal countries, to draw border lines unilaterally, and it is assumed that the Nine-Dash line drawn by China has no legitimate justification. The method of this research is descriptive-analytical and relying on library resources.