Mengzi is a city in the southeast of Yunnan Province, China. Administratively, it is a county-level city and the prefectural capital of the Honghe Hani and Yi Autonomous Prefecture, located about 243 kilometres (151 mi) southeast from Kunming, and 400 kilometres northwest from Hanoi, Vietnam. It is situated in the centre of a fertile valley basin on the Yunnan-Guizhou Plateau 1,310 metres (4,300 ft) above the sea level and was home to about 590,300 inhabitants as of 2021 census. Mengzi was formerly Mengzi County (蒙自县) until October 2010, when it was upgraded to a county-level city. Mengzi is the core area of South Yunnan Central City Cluster, which is officially regarded as the political, economic, cultural, and military centre of South Yunnan.

Honghe Hani and Yi Autonomous Prefecture is an autonomous prefecture in Southeast-Central Yunnan Province, China, bordering Vietnam's Lào Cai and Lai Châu provinces to the south. Its name is derived from the Hong (Red) River and the two major ethnic minority groups who live there: the Yi and the Hani. Honghe has an area of 32,929 square kilometres (12,714 sq mi) and its seat is Mengzi. The total population is 4.8 million, of which 61.3% belong to ethnic minorities.