The discovery of more than 350 new species has sparked calls to protect the rainforests in Borneo.
According to a WWF report, the forests need to be conserved not just for endangered species like orang-utans, but also for ones yet to be discovered.
Amongst the 361 new species found are the largest cockroach in the world, fish, frogs and lizards.
Large areas of Borneo's forest are being increasingly cleared for timber, rubber, and pulp and paper production.
"Borneo is undoubtedly one of the most important centres for wildlife in the world," said Tessa Robertson, head of the Forests Programme at WWF-UK.
"It is one of the only two places on earth where orang-utans, elephants and rhinos can be found."
The new report also suggests that thousands more undiscovered species may exist on Borneo, in the "heart" of the island, which is difficult to get to.