By the information of Catholic Hierarchy Catalog, there are 5,658,000 Catholics in Vietnam, representing 6.87% of the total population. There are 26 dioceses (including three archdioceses) with 2228 parishes and 2668 priests. .
The first Catholic missionaries visited Vietnam from Portugal at the beginning of the 16th century. The earliest missions did not bring very impressive results. Only after the arrival of Jesuits in the first decades of the 17th century did Christianity begin to establish its positions within the local population. Between 1627 and 1620 Fathers Alexander de Rhodes and Antoine Marquez of the French Province converted over 6,000, including numerous bonzes, who, during the temporary expulsion of the Jesuits dictated by the fear of their success, kept alive the faith. So rapidly did the Christian community increase that in 1659 the spiritual administration of Tong-king and Cochin China was entrusted to the first vicars Apostolic of the Society of Foreign Missions, who established parishes, built seminaries, and instituted many foundations of the Amantes de la Croix (i.e., Lovers of the Holy Cross).
Jesuit missionary Alexandre De Rhodes in the 17-th century created a written system of the Vietnamese language largely using the Roman alphabet with added diacritic markings, based on the work of earlier Portuguese missionaries. This system continues to be used today, and is called Quốc Ngữ (literally "national language").
By 1802, the Roman Catholic Church in Vietnam had 3 dioceses as follows:
Later centuries (mainly, 19th) had long periods of turbulence in Catholic life in Vietnam, including persecution of Roman Catholic clergy and ordinary believers by Vietnamese authorities. Such events described in Catholic Encyclopedia as the "Great Massacres", demonstrated, by the opinion of that encyclopedia, the fierce determination of the Annamite rulers to destroy every vestige of the Christian faith. In Eastern Cochin China the martyrs included 15 priests (7 native), 60 catechists, 270 nuns, 24,000 Christians (out of 41, 234); all the charitable institutions and ecclesiastical buildings of the mission—including the episcopal curia, churches, presbyteries, 2 seminaries, a printing establishment, 17 orphanages, 10 convents, and 225 chapels — were destroyed. In Southern Cochin China 10 native priests and 8585 Christians were massacred in the Quang Tri Province alone—the two remaining provinces supplied hundreds of martyrs; two-thirds of the churches, presbyteries, etc. of the mission were pillaged and burned. In the Mission of Southern Tong-king, 163 churches were burned; 4799 Catholics were executed, while 1181 died of hunger and misery. These figures apply only to the year 1885. In 1883-1884 eight French missionaries, one native priest, 63 catechists and 400 Christians were massacred in Western Tong-king, while 10,000 Catholics only saved themselves by flight. The carnage extended even to the remote forests of Laos, where seven missionaries, several native priests, and thousands of Catholics were killed.
The white and gold Vatican flag was regularly flown at all major public events in South Vietnam. U.S. Aid supplies tended to go to Catholics, and the newly constructed Hue and Dalat universities were placed under Catholic authority to foster a Catholic-skewed academic environment.
As demonstrations against his government continued throughout the summer, the special forces loyal to Diem's brother Nhu conducted an August raid of the Xa Loi Pagoda in Saigon. The pagodas were vandalised, monks beaten, the cremated remains of Thích Quảng Đức, which included a heart which did not disintegrate, were confiscated. Simultaneous raids were carried out across the country, with the Tu Dam Pagoda in Hue being looted, the statue of Gautama Buddha demolished and a body of a deceased monk confiscated. When the populace came to the defense of the monks, the resulting clashes saw 30 civilians killed and 200 wounded. In all 1400 monks were arrested, and some thirty were injured across the country.
In 1976, the Holy See made Archbishop Joseph Mary Trịnh Như Khuê the first Vietnamese cardinal. Joseph Mary Cardinal Trịnh Văn Căn in 1979 and Paul Joseph Cardinal Phạm Đình Tung in 1994 were his successors. The well known Vietnamese Cardinal Nguyên Văn Thuân, who was imprisoned by the Communist regime from 1975-1988 and spent nine years in solitary confinement, was nominated Secretary of the Pontifical Council for Justice and Peace, and made its President in 1998. On February 21, 2001 he was elevated to the College of Cardinals by Pope John Paul II.
Vietnam and the Vatican currently do not have diplomatic relations with one another. However, there have been meetings between leaders of the two states, including a visit by Vietnam's Prime Minister Nguyen Tan Dung to the Vatican to meet Pope Benedict XVI on January 25, 2007.
In March 2007, a Vatican delegation visited Vietnam and met with local officials. The sides discussed the possibility of establishing diplomatic relations in normal atmosphere, but have not provided a specific schedule for the exchange of ambassadors. The issues of continued restrictions on Catholic life in Vietnam and the nominating of bishops by the Pope without or with insisted by local government approval of Vietnamese bodies remain obstacles in bilateral dialog.
In March 2007, Thaddeus Nguyễn Văn Lý (b. 1946), a dissident Roman Catholic priest, was sentenced by Vietnamese court in Hue to eight years in prison on grounds of "anti-government activities". Nguyen, who had already spent 14 of the past 24 years in prison, was accused of being a founder of a pro-democracy movement Bloc 8406 and a member of the Progression Party of Vietnam.
On September 16, 2007, the fifth anniversary of the Cardinal Nguyễn Văn Thuận's death, the Roman Catholic Church began the beatification process for him. Pope Benedict XVI expressed "profound joy" at the news of the official opening of the beatification cause. Roman Catholics in Vietnam also reacted positively to the news of the opening of the Cardinal's beatification process.
In December 2007, thousands of Vietnamese Catholics marched in procession to the former apostolic nunciature in Hanoi and prayed there twice aiming to return the property to the local Church. The building was a historic Buddhist site until it was confiscated following the French colonisation of Vietnam, on grounds of protecting Catholics, before the communist North Vietnamese government confiscated it from the Vatican in 1959. That was evidently the first mass civil activity of the Vietnamese Catholics since the 1970s. A little later the protests were supported by Catholic faithful in Hồ Chí Minh City and Hà Ðông, who put forward the same demands for their respective territories. As a result in February 2008, the former building of the apostolic nunciature in Hanoi was promised by the Vietnamese Government to be returned to Roman Catholic Church. Though later in September 2008, the authorities changed their position and decided to demolish the building to create a public park
The dioceses are: