The Great Kei River is a river in the Eastern Cape province of South Africa. It is formed by the confluence of the Black Kei River and White Kei River, northeast of Cathcart. It flows for 320 km (199 mi) and ends in the at the Indian Ocean with the small town Kei Mouth on the west bank. Historically the Great Kei River formed the southwestern border of the Transkei region as was formerly known as the Nciba River.