The Tsushima Strait (対馬海峡) is a strait between Kyusyu, the westernmost of the four largest islands in Japan, or Iki Island and the Korean Peninsula . It connects the Sea of Japan and the East China Sea. The Japanese island Tsushima separates the strait into the West Channel (Korea Strait), between Tsushima Island and Korea Peninsula, and the East Channel, between Tsushima Island and Kyusyu or Iki Island.

This sea serves as a stage for cultural exchange between Japan and Korea. Buddhism was transmitted from Baekje to Japan through this strait. The Mongolian invasion of Japan crossed this sea and the Korean Allied Forces have attacked Japan through it. A decisive battle, the Battle of Tsushima, between the Japanese and Russian navies during the Russo-Japanese War also took place here. A ferry service operates between Shimonoseki and Busan now, and Japanese and Korean passengers are going back and forth.