Found in the northwest coast of the island of Borneo, Brunei Darussalam has a 130-kilometer coastline bordering the South China Sea, which consists of high-profile sandy beaches with a complex estuarine mangrove and mudflat zone in the northeast. The alluvial and often swampy coastal plain backed by low hills with swamps further inland characterizes the western part of the country. Meanwhile, the eastern part comprises a swampy coastal plain rising gradually to low hills to mountainous terrain inland.

The natural vegetation throughout the country is tropical evergreen rainforest. Forests cover 81 per cent of the total land area, of which 22 per cent is secondary forest and plantations, and 59 per cent primary forest. Forest reserves cover 41 per cent of the total land area, of which a quarter has now been allocated strictly for conservation.

The range of biodiversity in the country includes an estimated 15,000 species of vascular plants and an estimated 2,000 species of trees. There are about 100 non-flying mammal species, of which nearly half are rodents. Meanwhile, out of 390 species of animals recorded for the entire island of Borneo, more than 300 resident species can be found in Brunei, and majority of these are exclusive forest dwellers. Coral species are estimated to number about 400. Amphibian species count up to 98,while there are 50 species of reptiles. Freshwater fish are estimated at 50 species and marine fish at 144 species.