Kainan Maru (開南丸) was a converted fishing boat that was used as the expedition vessel during the Japanese Antarctic Expedition of 1910 to 1912. Substantially smaller than other expedition ships of the era, and with seriously underpowered auxiliary engines, she nevertheless completed a journey of some 50,000 km. After a false start in the southern summer of 1910–11, she entered the Ross Sea in January 1912 and landed a party on the Great Ice Barrier. While this party engaged in a southern march, Kainan Maru went to King Edward VII Land, where another party carried out survey and scientific work. The expedition returned to Japan with great acclaim in June 1912. However, it was quickly forgotten; Kainan Maru reverted to work as a fishing boat, and its subsequent career and fate remain unknown.

The Japanese Antarctic Expedition of 1910–12, in the ship Kainan Maru, was the first such expedition by a non-European nation. It was concurrent with two major Antarctic endeavours led respectively by Roald Amundsen and Robert Falcon Scott, and has been relatively overlooked in polar history. After failing to land in its first season, the Japanese expedition's original aim of reaching the South Pole was replaced by less ambitious objectives, and after a more successful second season it returned safely to Japan, without injury or loss of life.