Mbuji-Mayi or Mbujimayi is a city and the capital of Kasai-Oriental Province in the south-central Democratic Republic of Congo. It is thought to be the second largest city in the country, after the capital Kinshasa and ahead of Lubumbashi, Kisangani and Kananga, though its exact population is not known. Estimates range from a 2010 CIA World Factbook estimated population of 1,480,000 to as many as 3,500,000 estimated by the United Nations in 2008.

Kasaï-Oriental is one of the 21 new provinces of the Democratic Republic of the Congo created in the 2015 repartitioning. Kasaï-Oriental, Lomami, and Sankuru provinces are the result of the dismemberment of the former Kasaï-Oriental province. Kasaï-Oriental was formed from the Tshilenge district and the independently administered city of Mbuji-Mayi which retained its status as a provincial capital.