Being spread out in the Districts of Rathnapura, Galle & Matara, this majestic rainforest, Sinharaja Rainforest is one of the least disturbed and biologically unique lowland rainforest in Sri Lanka. With a length of 21km and a width of 7 km from North to south (at the widest point), the forest covers an extent of about 11187 hectares. It was declared a Man and Biosphere Reserve (MAB) in 1978,as representative of tropical humid evergreen forest Eco system in Sri Lanka and has been recognized by UNESCO as part of its International Network of Biosphere reserves. It was declared a National wilderness area in 1988 and lately a world heritage site in 1989.

Sinharaja Rainforest offers a huge diversity of species both flora and fauna with a large proportion of those being indigenous to the country and some more specifically endemic to Sinharaja itself. Because of the dense vegetation, wildlife is not as easily seen as at dry-zone national parks such as Yala. There are about 3 elephants and the 15 or so leopards are rarely seen. The commonest larger mammal is the endemic Purple-faced Langur. The Toque Monkey (Macaca sinica) is rare inside the forest but is more commonly observed in the peripheral areas. Several large mammals are characteristically terrestrial and feed off the forest floor. This group includes herbivorous browsers and mixed feeders, such as the Wild Pig (Sus scrofa), the Sambur (Cervus unicolour), Mouse Deer (Moschiola meminna) and Barking Deer (Muntiacus munjak).

An interesting phenomenon is that birds tend to move in mixed feeding flocks, invariably led by the fearless Greater Racket-tailed Drongo and the Noisy Orange-billed Babbler. Of Sri Lanka's 34 endemic birds, the 20 rainforest species all occur here, including the elusive Red-faced Malkoha, Green-billed Coucaland Sri Lanka Blue Magpie.

Reptiles include the endemic Green pit viper and Hump-nosed vipers, and there are a large variety of amphibians, especially tree frogs.  Some endemic species of lizards like Rough-horned Lizard (Ceratophoraaspera) and the Hump-nosed Lizard (Lyriocephalus scutatus) can be found in Sinharaja. Invertebrates include the endemic Common Birdwing butterfly and the inevitable leeches.

Sinharaja was a nominee for the 7 Wonders of the Nature of the World.