The Roman Catholic Diocese of Nkongsamba (Latin: Nkongsamben(sis)) is a Latin suffragan diocese in the ecclesiastical province of Douala in Cameroon.

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Its cathedral episcopal see is the Cathédrale de l’Immaculée Conception, dedicated to the Immaculate Conception at Nkongsamba, in Moungo Department in the Littoral Region (Cameroon).

As of 2014, it pastorally served 148,062 Catholics (42.4% of 349,270 total) on 4,057 km² in 505 parishes, 3 missions with 80 priests (67 diocesan, 13 religious), 130 lay religious (41 brothers, 89 sisters) and 40 seminarians.

Established on April 28, 1914, as Apostolic Prefecture of Adamaua, an immense territory on the Adamawa Pateau, split off from the much vaster still Apostolic Vicariate of Khartoum, in the then Anglo-Egyptian Sudan.

Renamed on June 11, 1923, as Apostolic Prefecture of Foumban, after its see F(o)umban.

Promoted on May 28, 1934, as Apostolic Vicariate of Foumban, hence entitled to a (titular) bishop.

It lost territory repeatedly :

• on May 28, 1940, to establish the Apostolic Prefecture of Berbérati (now a bishopric in Central African Republic)
• April 28, 1942, to establish the then Apostolic Prefecture of Niamey (in Niger)
• January 9, 1947, to establish the Apostolic Prefecture of Garoua and Apostolic Prefecture of Fort-Lamy (Chad)

On September 14, 1955, it was promoted and renamed as Diocese of Nkongsamba after its present see.

• Roman Catholicism in Cameroon