Hulunbuir is a region that is governed as a prefecture-level city in northeastern Inner Mongolia, in the People's Republic of China. Its administrative center is located at Hailar District, its largest urban area.
Until October 10, 2001, Hulun Buir was administered as a League. The area is 263,953 km2 (101,913 sq mi) and population 2.710 million as of 2004, while the gross domestic product was RMB 21.326 billion. The jurisdiction area of the city is actually larger than many Chinese provinces (and 42 U.S. states), and Hulun Buir is recognized as the largest city in the world by area, although the actual urban agglomeration is just a very small part of the region, and the average population density of the area is very low.

Major scenic features are the high steppes of the Hulun Buir grasslands, the Hulun and Buir lakes (the latter partially in Mongolia), and the Khingan range. Hulun Buir borders Russia, Mongolia, Heilongjiang province and Hinggan League.