South Korea, country in East Asia. It occupies the southern portion of the Korean peninsula. The country is bordered by the Democratic People’s Republic of Korea (North Korea) to the north, the East Sea (Sea of Japan) to the east, the East China Sea to the south, and the Yellow Sea to the west; to the southeast it is separated from the Japanese island of Tsushima by the Korea Strait. South Korea makes up about 45 percent of the peninsula’s land area. The capital is Seoul (Sŏul).