The diocese covers an area of 31,362 square kilometres (12,109 sq mi), covering four of the western
provinces of Thailand:
Ratchaburi,
Phetchaburi,
Kanchanaburi, and
Samut Songkhram. As of 2001, of the 2.2 million citizens, 15,246 are members of the Catholic Church. It is divided into 17 parishes, having 71 priests altogether.
The diocese dates back to 30 June 1930, when the
Mission sui iuris of Rajaburi was created, originally responsible for the south and west of Thailand, on territory split off from the then
Apostolic Vicariate of Bangkok (now its Metropolitan. It was run by the
Salesian order, who came there in 1927 and supplied the missionary Ordinaries. The 18 missionaries took over a mission previously run by the
Paris Foreign Missionaries.
On 18 December 1965 it became the Diocese of Bangnokhuek. On 21 October 1966 it was renamed Diocese of Ratburi.
On 26 June 1969 the
Diocese of Surat Thani was split off from the diocese (a fellow suffragan of Bangkok), which continued to be run by Salesians, while the remainder, again renamed
Diocese of Ratchaburi, was since then under the responsibility of native priests.

The cathedral of the diocese is the
Nativity of Our Lady Cathedral (Thai: อาสนวิหารแม่พระบังเกิด). It is in Bang Nok Khwaek,
Amphoe Bang Khonthi,
Samut Songkhram Province. The church is built in French Gothic style and decorated with stained glass windows imported from France. In two rows these show scenes of the life of Jesus in top row, as well as holy people (men to the north, women to the south).
Aroung 1840 nine Chinese Catholic families moved to the rim of the
Mae Klong River. The community grew to about 200 Catholics until 1847, when a first wooden church named Sala Daeng (Red Hall) or Raung Yao (Long Canal) was built near the site of the current cathedral. In 1850 Father Marin bought the land at the mouth of the
Khlong Damnoen Saduak and donated it to the church.
In 1890 the French missionary Father Paulo Salmon started construction of the Nativity of Our Lady church, which was inaugurated on 2 February 1896. During World War II several of the windows broke, which took until 1993 to be fully repaired. In 1994-1999 a major renovation of the cathedral was undertaken, overseen by Father Pradit.
Bishop John Bosco Panya Kritcharoen