Which island in Southeast Asia contains the largest remaining rainforest in Asia? Borneo contains it. The island’s vast tropical forests stretch across Indonesia’s Kalimantan, Malaysia’s Sabah and Sarawak, and Brunei, forming one of the world’s great rainforest strongholds.
Borneo is the third-largest island on Earth, covering roughly 743,000 square kilometres. Its rainforest is exceptionally old—often estimated at around 140 million years—and includes lowland dipterocarp forests, peat swamps, mangroves, and mountain forests. The Heart of Borneo, a transboundary conservation area, protects a major remaining block of this ecosystem.
Borneo is famous for species such as the Bornean orangutan, proboscis monkey, pygmy elephant, and rhinoceros hornbill. A common mix-up is Sumatra: it also has important rainforest and shares several species with Borneo, but Borneo is the larger island and holds Asia’s largest remaining rainforest block. The forests face pressure from logging, fires, mining, roads, and plantations.