The Sri Lanka lowland rain forests represents Sri Lanka's Tropical rainforests below 1,000 m (3,281 ft) in elevation in the southwestern part of the island. The year-around warm, wet climate together with thousands years of isolation from mainland India have resulted in the evolution of numerous plants and animal species that can only be found in rain forests in Sri Lanka. The thick forest canopy is made up of over 150 species of trees, some of the emergent layer reaching as high as 45 m (148 ft). The lowland rain forests accounts for 2.14 percent of Sri Lanka's land area. This ecoregion is the home of the jungle shrew, a small endemic mammal of Sri Lanka. Sri Lanka has the highest density of amphibian species worldwide. Many of these, including 250 species of tree frogs, live in these rain forests.

Sri Lanka exhibits a remarkable biological diversity and is considered to be the richest country in Asia in terms of species concentration.