Mangnai, also known as Mang'ai, is a county-level city in the northwest of Qinghai Province, China, bordering Xinjiang to the north and west. It is under the administration of Haixi Mongol and Tibetan Autonomous Prefecture. It is one of the most remote cities in China, the closest other city, Ruoqiang, is located 350 kilometres (220 mi) away. In 2020 it had a population of 18856. The name Mangnai is based on the Mongolian word for 'forehead'.

It was formed in 2018 when the Mangnai and Lenghu administrative zones merged to establish the county-level city of Mangnai.

Mangnai had a large asbestos mine, it was the largest in China, it also holds around half of China's serpentine reserves. It also produces oil, natural gas, celestite, and sodium sulfate.

Mangnai is divided into 3 towns. The administrative center is the Huatugou Town.

17 different ethnic groups live in the city, including the Han Chinese, Mongols, Tibetans, the Hui, Salars, Monguors, Manchus, Dongxiangs, and Uighurs.

Magnai has a cool arid climate (Köppen BWk), very similar to that of Golmud. It is characterised by warm to very warm summers, freezing to frigid winters, large diurnal temperature variation year-round, and extremely low precipitation especially in the cold season from October to April when only 4.9 millimetres or 0.19 inches can be expected in seven months.

The main touristic sites in Mangnai are:

In 2019, a camp meant to simulate conditions on the planet Mars opened in the town of Lenghu, which is primarily geared towards tourists.