Kuala Belait (KB) or officially the Kuala Belait Town (Malay: Pekan Kuala Belait), is the administrative town of Belait District, Brunei. The population of the town proper was 4,544 in 2021. Kuala Belait is officially a municipal area (kawasan bandaran), as well as a settlement under the mukim of the same name. The town is located 85 kilometres (53 mi) west of the country's capital Bandar Seri Begawan, and 20 kilometres (12 mi) west of Seria, the district's other town. It is also in the westernmost part of country, near the mouth of the Belait River.

The name "Kuala Belait" originates from the Malay words kuala, meaning "river mouth" or "confluence," and Belait, referring to the Belait River and the indigenous Belait people who inhabit the region. This naming reflects the town's geographical position at the mouth of the Belait River, where it empties into the South China Sea. As with other kuala settlements, the location was likely chosen for its strategic significance, offering both defensive advantages and accessibility for trade and transportation along the river and coastal routes.

Before 1909, Kuala Belait was a small fishing village with little development. Although oil exploration began in the Belait District as early as 1911, and some oil was found in Labi in 1914, it had minimal impact on Kuala Belait’s growth at that time. However, the discovery of oil in Labi convinced prospectors that further deposits might be found along the higher banks of the Belait River. That same year, a 60-mile (97 km) road was constructed, linking Kuala Belait to Brunei Town.

Oil companies began concentrating their activities in the area, leading to the emergence of a thriving village in Kuala Belait by 1927. At the time, it served as a port for transporting machinery crucial to oil prospecting, primarily managed by the British Malayan Petroleum Company (BMPC). Kuala Belait soon became a key entry point to the upper reaches of the Belait River, and the government recognised its growing significance by establishing it as the headquarters of the Belait District that same year. In 1929, BMPC followed suit by relocating its headquarters to Kuala Belait, further boosting the village's development. The discovery of large oil reserves in Seria, in April 1929, significantly increased Kuala Belait's importance as a strategic hub for the oil industry. In that same year, Kuala Belait became a town after the establishment of the Kuala Belait Sanitary Board, which is run by the Assistant British Resident.

The 1930s marked a period of rapid growth for Kuala Belait, largely driven by the BMPC. In 1931, the town became the site of Brunei's first English school, and it also boasted the best hospital in the country at the time. Its population grew significantly, from 1,193 in 1931 to 3,000 by 1935, fueled by the thriving oil industry. Despite this progress, the town was heavily bombed during World War II, leading to widespread destruction and the need to rebuild. The BMPC also played a crucial role in infrastructure development, constructing a telephone line along the Belait coastline earlier in 1930, linking Seria and Rasau to their headquarters in Kuala Belait. However, a telephone line connecting Kuala Belait to Tutong was dismantled in 1934 after failing to meet expectations. By 1939, pipelines and roads between Kuala Belait and Miri had been established, further enhancing the town's connectivity and industrial growth.

On 16 December 1941, Kuala Belait was captured after an amphibious assault on the Belait coast by 10,000 soldiers from the Japanese Kawaguchi Detachment. The town remained under Japanese occupation during World War II. During this time, war crimes were committed by the Japanese, including the massacre and execution of Indian prisoners of wars (POW) from the 2/15th Punjab Regiment. Additionally, 55 Indian prisoners died from starvation in the town's POW camp. As part of Operation Oboe Six, the Australian 9th Division arrived in Kuala Belait on 24 June 1945, leading to the recapture of the port. In 1949, reconstruction plans for the war-torn town were approved.

Kuala Belait experienced significant growth during the 1950s and 1960s, driven by increased revenue from the booming oil industry. The Sanitary Board was upgraded to the Municipal Board in 1953. The discovery of the first offshore gas field, South West Ampa, located 13 kilometres (8.1 mi) off Kuala Belait in 1963, further boosted the town's growth. During the 1962 Brunei revolt, TKNU rebels briefly gained control of the town, but the town was soon liberated by the 1/2nd Battalion Gurkha Rifles Regiment, with local police successfully defending the police station.

After Brunei's independence in 1984, several new government buildings were constructed to house local services. In the 1990s, the coastal road from Muara to Kuala Belait was upgraded to a four-lane highway, further enhancing the town's infrastructure. The Municipal Board was overseen by the Belait District Officer from 31 October 1985. From 1 November 1985, the municipality has been administered by a chairman. By 1997, it had become Brunei's second-largest town, following Bandar Seri Begawan. Often referred to as a "Shell town," much of its postwar development was attributed to Shell's efforts.

The area of Kuala Belait comprises territorial division which can be informally grouped into three main areas: Pekan Kuala Belait or Kuala Belait Town, and Kampong Pandan and Mumong suburbs. The latter two areas are further divided into three and two kampongs or villages respectively. Pekan Kuala Belait is also officially a kampong-level administrative division. All of the villages constitute almost all of Mukim Kuala Belait, a subdistrict of Belait.

The town of Kuala Belait is administered under Jabatan Bandaran Kuala Belait dan Seria (Kuala Belait and Seria Municipal Department), a government department under Kementerian Hal Ehwal Dalam Negeri (the Ministry of Home Affairs). The department comprises Lembaga Bandaran or the Municipal Board, which is headed by Pengerusi Lembaga Bandaran (Chairman of the Municipal Board). The current chairman is Ridzuan Haji Ahmad.

The area under the authority of the Municipal Department overlaps with that under Jabatan Daerah Belait or the Belait District Office. The municipal area consists of Pekan Kuala Belait, the whole of Kampong Pandan suburb, and parts of Mumong suburb. However, all of the kampongs are also under the governance of the Belait District Office, since they constitute the proper subdivisions of the district and subdistricts, and subsequently the headmen of the kampongs, known as ketua kampong (with the exception of Pekan Kuala Belait since there is none assigned), answers to the Pegawai Daerah or District Officer.

Kuala Belait is located in the vicinity of the onshore Rasau gas field. However Brunei Shell has various facilities in town to support the oil and gas production facilities in the vicinity.

The Kuala Belait Bunkering Station (KBBS) is located near the mouth of the Belait River. It supplies domestic gas to the town and other bulk chemicals in support of the various activities. The Kuala Belait Wharf is the main point from which personnel to and from the offshore platforms, off the Belait districts, embark and disembark.

The Kuala Belait supply base is located to the south of the wharf, and is the main point for logistics for Shell. The Marine Construction Yard (MCY) in Sungai Duhon, commonly known as SCO, is where construction of marine structures are carried out prior to installation offshore.

Kampong Kuala Balai has historically served as the Belait population's hub. However, the population has scattered over the past 50 years, and now, Belait tribe members may be found in and around the town. By 1938, Kuala Belait's population had increased to 5,000, and the BMPC was the city's major employer, with 1,185 out of 2,265 workers under its payroll. 1,193 people were counted in Kuala Belait at the time of the 1931 census. It was reportedly 12,000 in 1948, due to the development around the district's oilfield. The town has a sizable Chinese population, and most Europeans are concentrated in Kuala Belait and Seria.

The climate of Kuala Belait is tropical. The weather is warm, humid and rainy all year.

Month	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Average High (°C)	31	31	32	33	33	33	33	33	32	32	32	32	-
Average Low (°C)	24	24	24	24	24	24	24	24	24	24	24	24	-
Average Rainfall (mm)	360	200	190	287	288	226	196	219	250	284	260	297	3045

Road transportation in Kuala Belait has evolved significantly, particularly following the discovery of oil. Initially, communication with the capital was challenging, as access by land required traveling along the beach between Kuala Belait and Tutong, where a road existed. In 1931, the appointment of an assistant British Resident marked a turning point, although land connections with Brunei Town remained difficult. The BMPC played a crucial role in enhancing road infrastructure, providing necessary improvements to support the growing immigrant population associated with the oilfields. By 1938, the population of Kuala Belait had reached 5,000, with the BMPC being the largest employer in the district and continuing to invest in local infrastructure. In the 21st century, most roads in Kuala Belait are surfaced, and there are bus services transporting passengers to Miri. The Lumut–Belait Highway connects the Malaysian border west of Sungai Tujoh with various highways that lead to Bandar Seri Begawan and Muara town.

Water transportation has historically been vital for Kuala Belait, particularly before the improvement of road infrastructure. Initially, communication with the capital was primarily by sea and via Labuan, as the Belait River was closed for six months each year due to the monsoon, which hindered trade. This reliance on water routes limited the movement of goods and people until road access improved. The BMPC contributed significantly to the development of water transport facilities by establishing wharves to facilitate the movement of materials and personnel to and from the oilfields. Despite these advancements, the oilfield community in Brunei often had closer contact with the oilfield community in Sarawak, where oil was piped for refining, highlighting the ongoing importance of water transportation in the region.

Water transportation in Kuala Belait is facilitated by a public wharf near the market, where visitors can hire water taxis to travel upriver towards Kuala Balai. Additionally, the Kuala Belait Boat Club organizses trips for sailing out to the open sea and visiting various nearby destinations. Historically, a timber jetty existed in Rasau as early as 1930. The Kuala Belait Port, one of Brunei's three ports, has sections near the river mouth operated by Brunei Shell, restricting public access. The commercial port is situated further upriver in Kampong Sungai Duhon and surrounding areas. However, due to silting at the river mouth, the port can only accommodate shallow draft vessels. To combat this issue, two breakwaters have been constructed at the mouth of the Belait River to help reduce silting.

The town is also home to the Consulate of Mexico and St. John's Church.

Primary education is offered in various government and private schools. There are currently three government primary schools:

• Ahmad Tajuddin Primary School
• Paduka Seri Begawan Sultan Omar Ali Saifuddien Primary School
• Pengiran Setia Jaya Pengiran Abdul Momin Primary School

The government also has built three schools which offer secondary education:

• Perdana Wazir Secondary School
• Pengiran Jaya Negara Pengiran Haji Abu Bakar Secondary School (SMPJNPHAB)
• Sayyidina Ali Secondary School

There are four private schools in Kuala Belait. They may offer primary, secondary or both.

• Chung Hua Middle School, Kuala Belait
• International School Brunei, Kuala Belait
• St. James' School
• St. John's School

Secondary students opting for sixth form education study at Pusat Tingkatan Enam Belait. Alternatively, students opting for vocational education may proceed to study at one of the two post-secondary institution, namely:

• Institute of Brunei Technical Education, Jefri Bolkiah Campus – a government post-secondary institution providing technical and vocational qualifications; and
• Kemuda Institute – a private college that offers Foundation, Diploma and Advanced Diploma courses.

Kuala Belait town itself has a number of tourist attractions. Some of these are:

• Silver Jubilee Park is a park built to commemorate the Silver Jubilee of Sultan Hassanal Bolkiah’s accession to the throne, as a gift from the people of Kuala Belait.
• Menara Cendera Kenangan is a monument built to commemorate the Sultan Hassanal Bolkiah's 50th Birthday, along the Belait River.
• Tea Pot Roundabout (locally known as 'kiri') is a monument in Kampong Pandan sponsored by Brunei Shell Petroleum.
• Belait District Museum is a museum dedicated to the Belait District.
• Kampong Pandan Mosque is a mosque in Kampong Pandan, built in 1994.
• Mohammad Jamalul Alam Mosque is a mosque in Kampong Melayu, built in 1961.
• Istana Kota Manggalela is the residence of the Sultan of Brunei in the Belait District, completed in 1958.
• Kuala Belait Library
• Belait Beach lies along the coast of Kuala Belait.

• Yusoff Abdul Hamid (born 1949), politician and diplomat
• Maizurah Abdul Rahim (born 1999), sprinter
• Abu Sufian Ali (born 1966), diplomat
• Salleh Bostaman, businessman and politician
• Johnie Everett (born 1964), Scottish cricketer
• Abdul Hariz Herman (born 2000), footballer for MS ABDB
• Hong Kok Tin (1910–1989), businessman and aristocrat
• Adinin Ibrahim (1932–2023), businessman
• Jefri Syafiq Ishak (born 2002), footballer for Kuala Belait FC
• Princess Jaga (died 1967), daughter of Sultan Hashim Jalilul Alam Aqamaddin
• Christina Koning, novelist and writer
• Tiger Lim (born 1974), blogger and YouTube comedian
• Ng Teck Hock (1928–2008), nobleman
• Suyoi Osman (born 1952), politician and minister
• Adina Othman (born 1955), bureaucrat
• Zulkhairy Razali (born 1996), footballer who plays striker for Indera SC

• 
  Belait Beach
• 
  Menara Cendera Kenangan
• 
  Mohammad Jamalul Alam Mosque
• 
  Silver Jubilee Park
• 
  Istana Kota Manggalela
• 
  Kuala Belait Library
• 
  Mumong Sports Complex
• 
  Tudung Saji
• 
  V Plaza Hotel
• 
  Belait Arabic School
• 
  Kuala Belait Fire Station

• Mikoley, Kate (2022). Cultures of the World: Brunei. London: Cavendish Square Publishing. ISBN 978-1-5026-6307-8.
• Malone, Paul (2020). Kill the Major: The true story of the most successful Allied guerrilla war in Borneo. For Pity Sake Publishing. ISBN 978-0-6487587-4-7.
• Pratten, Garth (2016). Australia 1944–45: Victory in the Pacific. Port Melbourne: Cambridge University Press. ISBN 978-1-107-08346-2.
• Cleary, Mark; Wong, Shuang Yann (2016). Oil, Economic Development and Diversification in Brunei Darussalam. Springer. ISBN 978-1-349-23485-1.
• Ooi, Keat Gin (2013-05-29). Post-War Borneo, 1945-1950: Nationalism, Empire and State-Building. Routledge. p. 1950. ISBN 978-1-134-05810-5.
• Felton, Mark (2010-06-19). The Final Betrayal: MacArthur and the Tragedy of Japanese POWs. Pen and Sword. ISBN 978-1-84468-478-6.
• James, David H. (2010). The Rise and Fall of the Japanese Empire. Vol. 35. Abingdon and New York: Routledge. ISBN 978-1-136-92547-4.
• Ooi, Keat Gin (2004). Southeast Asia: A Historical Encyclopedia, from Angkor Wat to East Timor. ABC-CLIO. ISBN 978-1-57607-770-2.
• Saunders, Graham (2003). A History of Brunei (2nd ed.). London and New York: RoutledgeCurzon. ISBN 9781138863453.
• Airriess, Christopher A. (2003). "The Ecologies of "Kuala" and "Muara" Settlements in the Pre-Modern Malay Culture World". Journal of the Malaysian Branch of the Royal Asiatic Society. 76 (1 (284)): 81–98. ISSN 0126-7353.
• Singh, D. S. Ranjit; Sidhu, Jatswan S. (1997). Historical Dictionary of Brunei Darussalam. London: Scarecrow Press. pp. 79–80. ISBN 9780810832763.
• Europa Publications Limited (1995). The Far East and Australasia 1995 (26th ed.). London Europa Publications.
• Shariffuddin, P. M.; Omar, Hj. Matussin, eds. (1994). The Brunei Museum Journal. Bandar Seri Begawan: The Brunei Museums Department, Ministry of Culture, Youth and Sports.
• Ness, Gayl D. (1962). Letters from Southeast Asia to the Institute of Current World Affairs.
• Great Britain Colonial Office (1955). State of Brunei Annual Report 1955.
• Great Britain Colonial Office (1936). Report of the State of Brunei for the Year 1936. London: Her Majesty's Stationery Office.
• Great Britain Colonial Office (1930). Report of the State of Brunei for the Year 1930. London: Her Majesty's Stationery Office.

• Kuala Belait Municipal Board
• KEMUDA Institute