Eusideroxylon is a genus of evergreen trees of the family Lauraceae. The genus is monotypic, and includes one accepted species, Eusideroxylon zwageri. The species is commonly known as Bornean ironwood, or by the Malay names belian and ulin. It is predominantly found in Borneo and Sumatra, where it grows in lowland rain forests, but is also thought to inhabit the Philippines.

Eusideroxylon are hardwood trees reaching up to 50 metres (160 ft) in height with trunks over 2 metres (6 ft 7 in) in diameter, producing commercially valuable timber. The wood of E. zwageri is impervious to termites, and can last up to 100 years in contact with the ground. Due to extensive logging, it is listed as vulnerable in the IUCN Red List.

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