Kasai (käsī´), former province, c.124,000 sq mi (321,160 sq km), S central Congo (Kinshasa). Luluabourg (present Kananga) was the capital. Between the Kasai and the Sankuru rivers the Kuba kingdom of the Shongo people existed from the early 17th cent. In the south of the province were the constantly warring Luba and Bena Lulua peoples. This ethnic conflict was partly responsible for the secession (Aug., 1960) of the Baluba-dominated Mining State of South Kasai, headed by Albert Kalonji, who proclaimed himself king of South Kasai. The central government reestablished control over the whole of Kasai in Dec., 1961. The region is now divided into Kasai-Occidental and Kasai-Oriental provinces.

Kasai or Cassai, river, c.1,100 mi (1,800 km) long, rising in central Angola, S central Africa, flowing E, N, and NW through W Congo (Kinshasa) to the Congo River; it forms part of the Angola-Congo border. The Kasai, navigable for c.475 mi (760 km) above its mouth, is an important trade artery. Its tributaries include many navigable streams (some of which are rich in alluvial diamonds).