The diocesan territory covers a land area of 4,948.2 square kilometers. It includes Ratnapura and Kegalle districts of Sri Lanka.
The population of the diocese is 1,968,000 (the population of the whole country 21,670,000), Most residents are Sinhalese, estimated 1,266,091. 86.42% of them are Buddhists and 9.88% Hindus.
The Sinhala and Tamil languages are in use.
The history of Catholics in Ratnapura begins with Portuguese rule in Ratnapura in 17th century and very few catholics. Many of them were the descendents of Portuguese and locals that they married. Blessed Joseph Vaz, the Apostle of Sri Lanka, had visited the place where now Sts. Peter and Paul Cathedral is located when he came to Ratnapura as part of his apostolic mission.
The diocese of Ratnapura is dedicated to Sts. Peter and Paul.
Ratnapura diocese is adjacent to Kurunegalla in the north, Badulla in the east, Colombo in the west and Galle in the south.
The birthday of Ratnapura diocese is on Nov. 2, 1995. It was taken out from the territory of Galle diocese. Bishop Patabendige Don Albert Malcolm Ranjith (1995-2001), currently secretary of the Vatican's Congregation for Divine Worship and the Discipline of the Sacraments, was the first bishop. He was followed by Bishop Harold Anthony Perera (2003 - 2005). Now Bishop Cletus Chandrasiri Perera O.S.B heads Ratnapura diocese. There are 21,855 baptized Catholics, of all 1,787,938 people in the territory. Ratnapura has 23 parishes with 27 resident priests.
Ratnapura diocese is located in the south-western part of Sri Lanka, the so-called wet zone.The diocese receives rainfall mainly from south-western monsoons during May to September. The average temperature is 24 degrees Celsius, and there are high humidity levels.
Ratnapura is called "City of Gems".The city is located about 100 kilometers south-west of Colombo, it is the centre of a long-established industry of precious stone mining including rubies, sapphires and other gems.
Most of the people depend on the gem trade. Gem pits are a common sight in the area. Most of the large-scale gem businessmen of Sri Lanka operate from Ratnapura. Precious stones, rubies, sapphires and various kinds of gemstones are available here.
Agro based industries like tea rubber coco are here. Large plantations of tea and rubber surround the town. Tea grown in this region is called low-country tea.
Sinharaja rain forest, Uda Walawe National Park, covers a large area in the region.
Bopath waterfall and Rajana waterfall beautify the area and there are many places of worship in and around this area such as Maha Saman Devala (Buddhist), St.Luke (Church of England), Siva Temple (Hindu) and Jumma Mosque (Islam).
Ratnapura is situated in the flooding plain of the river Kalu and the town experiences regular floods usually in the month of May. There is no large dam across the Kalu. In May 2003, the town experienced the largest flood since the independence of Sri Lanka from Britain in 1947.