Kopsia rajangensis is a tree in the family Apocynaceae. The specific epithet rajangensis refers to the Rajang River in Borneo, near which the species was initially surveyed.
Kopsia rajangensis grows as a shrub or small tree up to 5m (16feet) tall. Its flowers feature a white corolla.
Kopsia rajangensis is endemic to Borneo, where it is confined to Sarawak. Its habitat is hill forests.