Abstract: According to a series of important historical maps,i.e.,"Location Map of the South China Sea Islands,Nansha Islands,Zhongsha Islands,Xisha Islands,Yongxing Island and Stone Island,Taiping Island" (drafted by the Internal Ministry of Republic of China in 1946) and "Administration District Map of Republic of China" (published in 1948),the dashed line surrounding the South China Sea Islands represents the determinate maritime boundary of the Republic China. It was shown in these maps that the dashed line is the clear extension of the solid line of China boundary. It should be noted that it was internationally accepted by the worldwide nations and scientific societies that the dashed line was used as the maritime boundary while the solid line was used as the land boundary of a nation. The findings in this work provide historical and scientific evidence for international maritime delimitation over the South China Sea.