city and capital of Hainan (Hai-nan) sheng (province), southern China. It is situated on the north coast of Hainan Island, facing the Leizhou Peninsula, across the Hainan (Qiongzhou) Strait (9.5 miles 【15 km】 wide). Haikou originally grew up as the port for Qiongshan, the ancient administrative capital of Hainan Island, which is situated some 3 miles (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 harbour, 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, and it has replaced Qiongshan as the island's administrative capital. It exports great quantities of agricultural produce and livestock. In 1988 Hainan was made a province, having been set off from Guangdong and designated as an economic development zone, the largest area of its kind. Since then Haikou has experienced a period of rapid economic and floating population growth. The infrastructure of the city has been rapidly improved. Haikou is linked to Sanya and other cities of the island by an expressway. The city's international airport has flights to other major cities in China, as well as to Thailand, Singapore, and other Southeast Asian countries. Food processing and the manufacture of rubber goods, electronics, and machinery are the major industries of Haikou. Pop. (2002 est.) 533,960.