In a land area of 7,136 square kilometers, the diocesan territory covers three districts namely Manggarai, West Manggarai, and East Manggarai. It borders with Sape strait in the west, Archdiocese of Ende in the east, Flores Sea in the north, and Sawu Sea in the south.
Catholics in the diocese consist mostly of Flores people and a few of Javanese people.
During 1910-1911, Jesuit missioners had visited the west of Manggarai. On May 17, 1912, Jesuit Father P. Loojmans baptized the first Catholics in Reo, including Katarina (Arbero), Henricus, Agnes Mina, Caecilia Weloe, and Helena Loekoe.
Divine Word missionaries then came to Ruteng in 1914. Several mission stations were established in 1929-1957.
In 1925, there were 7,036 Catholics in two parishes. On Sept. 29, 1929, the deanery of Manggarai was established and Divine Word Father Thomas Koning served as the dean. In 1929, Catholics began building the cathedral and finished it in 1931. On March 8, 1951, the deanery of Manggarai was elevated into Apostolic Vicariate of Ruteng. Divine Father Wihelmus van Bekkum was chosen as the apostolic vicar. The priest was then ordained a bishop on May 13, 1951.
On Jan. 3, 1961, the apostolic vicariate of Ruteng was elevated into diocese. Divine Word Bishop Wihelmus van Bekkum served as its first bishop. He retired on Jan. 31, 1972.
Divine Father Vitalis Djebarus was chosen as his successor and ordained as the second Bishop of Ruteng on May 5, 1973. However, the bishop was then appointed as the Bishop of Denpasar Diocese in 1981.
On Dec. 3, 1984, Holy See appointed Divine Word Father Eduardus Sangsun as the Bishop of Ruteng. His Episcopal ordination was on March 25, 1985. The bishop passed away on Oct. 14, 2008. Father Laurens Sopang has since served as diocesan administrator.