The Roman Catholic Diocese of Ambanja (Latin: Ambaniaën[sis]) is a diocese located in the city of Ambanja in the ecclesiastical province of the Metropolitan Archdiocese of Antsiranana in Madagascar. Its episcopal see is the Cathedral of Saint Joseph, which was constructed in 1933.

On September 4, 1848, the Apostolic Prefecture of Isole di Mayotta, Nossi-Bé e Comore was established from the Apostolic Vicariate of Madagascar. In 1843 the French Government, called in by the sultan, had taken possession of Mayotte, which became, with Nossi-Bé, a post of surveillance over Madagascar. These islands later formed a French colony, with a population largely Muslim. Mayotte, Nossi-Bé and the Comoros were made an Apostolic prefecture and confided to the Fathers of the Holy Ghost.

In 1898, when the same missionaries were given the ecclesiastical administration of Northern Madagascar, these smaller islands and Santa Maria were attached to the then Apostolic Vicariate of Diégo-Suarez. Santa Maria and Nossi-Bé had resident missionaries.

• June 14, 1938: Renamed as Apostolic Prefecture of Ambanja
• Promoted on March 8, 1951 as Apostolic Vicariate of Ambanja
• Promoted on September 14, 1955 as Diocese of Ambanja, yet remains dependent in Rome on the missionary Congregation for the Evangelization of Peoples
• On 5 June 1975, it lost its original missionary territory (modern Comoros and Mayotte) to establish the exempt Apostolic Administration of the Comoros Archipelago.

all Roman Rite (Latin)

Apostolic Prefect of Mayotte, Nosy-Be and Comore

• Friar Callisto Lopinot, OFMCap (1932.05.15 – 1937)

Apostolic Prefect of Ambanja

• Fr. Léon-Adolphe Messmer, OFMCap (1937.11.12 – 1951.03.08 see below)

Apostolic Vicar of Ambanja

• Bishop Léon-Adolphe Messmer, OFMCap, Titular Bishop of Coropissus (see above 1951.03.08 – 1955.09.14 see below)

Suffragan Bishops of Ambanja

• Léon-Adolphe Messmer, OFMCap (see above 1955.09.14 – 1975.06.05), later permanent Apostolic Administrator of Comores (Comoros) (1975.06.05 – 1980.05.02)
• Ferdinand Botsy, OFMCap (1976.07.08 – 1997.10.25)
• Odon Marie Arsène Razanakolona (1998.11.28 – 2005.12.07), later Metropolitan Archbishop of Antananarivo (Madagascar) (2005.12.07 – ...),
  • remaining Apostolic Administrator (2005.12.07 – 2007.11.07)
• Rosario Saro Vella, SDB (2007.11.07 – 2019.07.08), appointed Bishop of Moramanga
• Donatien Francis Randriamalala, MS (2022.11.11 – ...)

• Roman Catholicism in Madagascar

• GCatholic.org with incumbent bio links
• Catholic Hierarchy

13°40′43″S 48°27′08″E / 13.67861°S 48.45222°E / -13.67861; 48.45222