Haixi Mongolian and Tibetan Autonomous Prefecture (; ; ), locally also known as Qaidam Prefecture (; ; ), is an autonomous prefecture occupying much of the northern half of (as well as part of the southwest of) Qinghai Province, China. It has an area of and its seat is Delingha. The name of the prefecture literally means "west of (Qinghai) Lake."
Geladandong Mountain, the source of the Yangtze River, is located here.
After 1949, the People's Government of Dulan County was founded and the area was renamed Dulan Autonomous District (); in 1954, Dulan was renamed Haixi Mongol, Tibetan and Kazakh Autonomous District () and in 1955, Haixi Mongol, Tibetan and Kazakh Autonomous Prefecture (). In 1963, it was renamed "" (with the "Tibetan" added to the official county name). In 1985, after the Kazakhs had returned to Xinjiang, it was again renamed to Haixi Mongol and Tibetan Autonomous Prefecture.
As of the 2017 census, Haixi had 515,200 inhabitants.
The following is a composition of ethnic groups in the prefecture, taken in the 2010 Census.
Haixi directly governs 3 county-level cities and 3 counties.