Nain (Persian: نائین)[a] is a city in the Central District of Nain County, Isfahan province, Iran, serving as capital of both the county and the district.

[4] The history of Nain appears to go back to pre-Islamic times, but no information about it has survived.

It was described by medieval historians to have been in the sardsīr ("cooler highland areas"), and being a subordinate to either Yazd or Isfahan, despite being part of the administration of the Fars province.

The historian and geographer Hamdallah Mustawfi reported that the walls of Nain's castle, which are still present as mud brick remnants, were four thousand paces long.

During the Safavid era, the kaolinite of Nain was utilized to manufacture porcelain at the city of Kashan.