Haikou situated at the north of Hainan island, is the capital of Hainan Province of the People's Republic of China and has an estimated population of 830,192 (2006), therefore by far the largest city on the island.

Haikou originally grew up as the port for Qiongshan, the ancient administrative capital of Hainan Island, which is situated some 5 km inland. It became a military post in the 13th century and was fortified under the Ming dynasty (1368–1644). The port is situated to the west of the mouth of the Nandu, Hainan's chief river. Although it has no good natural harbor, it has always been the principal port of the island.

After Qiongshan was opened to foreign trade under the Treaty of Tianjin (1876), Haikou began to rival the old administrative city. Haikou was created a separate administrative county in 1926; it overtook Qiongshan in population in the 1930s.

Haikou was much developed as a port during the Sino-Japanese War (1937–45) when the Japanese occupied Hainan Island from early 1939 to 1945. Since 1949, Haikou has retained its position as Hainan's main port, handling more than half of its total trade; it has replaced Qiongshan as the island's administrative capital.

Haikou was made a prefecture-level city as well as the capital of the newly-created Hainan Province in 1988.

Haikou has an area of 2,304.84 square kilometers.[1] It is situated on the north coast of Hainan Island, facing the Leizhou Peninsula, across the Hainan Strait (15 km wide); in an area that reaches from Zengmu Ansha in the south to the Qiongzhou Strait in the north; bordering the sea areas of the South China Sea and facing Vietnam in the west across Beibu Bay.