Christianity, introduced into Cambodia by Roman Catholic missionaries in 1660, made little headway, at least among the Buddhists. In 1972 there were probably about 20,000 Christians in Cambodia, most of whom were Roman Catholics.
Before the repatriation of the Vietnamese in 1970 and 1971, possibly as many as 62,000 Christians lived in Cambodia. According to Vatican statistics, in 1953, members of the Roman Catholic Church in Cambodia numbered 120,000, making it, at the time, the second largest religion in the country. In April 1970, just before repatriation, estimates indicate that about 50,000 Catholics were Vietnamese. Many of the Catholics remaining in Cambodia in 1972 were Europeans--chiefly French. Steinberg reported, also in 1953, that an American Unitarian mission maintained a teacher-training school in Phnom Penh, and Baptist missions functioned in Batdambang and Siemreab provinces. A Christian and Missionary Alliance mission was founded in Cambodia in 1923; by 1962 the mission had converted about 2,000 people. American Protestant missionary activity increased in Cambodia, especially among some of the hill tribes and among the Cham, after the establishment of the Khmer Republic. The 1962 census, which reported 2,000 Protestants in Cambodia, remains the most recent statistic for the group. In 1982 French geographer Jean Delvert reported that three Christian villages existed in Cambodia, but he gave no indication of the size, location, or type of any of them. Observers reported that in 1980 there were more registered Khmer Christians among the refugees in camps in Thailand than in all of Cambodia before 1970. Kiernan notes that, until June 1980, five weekly Protestant services were held in Phnom Penh by a Khmer pastor, but that they had been reduced to a single weekly service after police harassment. His estimates suggest that in 1987 the Christian community in Cambodia had shrunk to only a few thousand members.
There are around 20,000 Catholics in Cambodia which represents only 0.15% of the total population. There are no dioceses, but there are three territorial jurisdictions - one Apostolic Vicariate and two Apostolic Prefectures.