In the middle of the nineteenth century, the Kingdom of Cambodia was destroyed by war and the Catholic communities were almost annihilated.  On August 30, 1850 the Holy See created the Apostolic Vicariate of Phnom Penh which covered the Kingdom of Cambodia. That year, the Holy See appointed Mgr Jean-Claude Miche to be the Apostolic Vicar of Phnom Penh. From 1870 up to 1955, three provinces of Lower Cambodia, namely Sadec, Chaudoc and Soctrang were placed under the care of the Apostolic Vicar of Phnom Penh.
In 1866 King Norodom had the Khmer Catholics leave Ponhea Lu and go to the  capital, Phnom Penh, where they were given land to build their church in Prek Luong.
In 1881 the Sisters of Providence of Portieux began their house in Phnom Penh. During the French Protectorate, many Catholics from Vietnam came and settled down in Cambodia.
In 1952 a monastery of the Benedictine monks from LA PIERRE-QUI-VLRE, France, was built in Kep in Kampot province. Tn 1957 the first Khmer priest was ordained.
On September 26, 1968 the Holy See divided the Apostolic Vicariate of Phnom Penh into three Ecclesiastical Circumscriptions namely Phnom Penh, Battambang and Kompong Cham.  Mgr Paul Tep Im Sotha became the Apostolic Prefect of Battambang.
In 1970 the Catholic community organized an Aid commission to help the victims of war. This relief commission soon became important and took the name of  "Caritas Cambodge"
On April 14, 1975 Mgr Joseph Chhmar Salas was made Bishop Coadjutor of the Apostolic Vicar of Phnom Penh.
Bishop Joseph Chhmar Salas, Mgr. Paul Tep Im Sotha, all Khmer priests, religious and a great number of Khmer Catholics lost their lives during the years of the genocide. Most churches (not Kompong Som, Chomnon and convents) were destroyed. On April 4, 1990 the Catholic communities were given
the government permission to worship freely, thanks to efforts of Fr. Emile Destombes.
Nowadays the Apostolic Vicariate of Phnom Penh Comprises Phnom Penh  city, Sihanoukville, the
provinces of Kandal, Takeo, Kampot, Kompong Speu and Koh-Kong.
The Prefecture of Battamhang covers eight provinces, namely Battambang, Pursat, Kompong Chhnang,
Kompong Them, Siem Reap, Preah Vihear, Oddar Meanchey and Banteay Meanchey.
The Prefecture of Kompong Cham provinces: Kompong Cham,  Kratie Prey  Veng,   Stoeung Treng, Mondulkiri.