Castanopsis oligoneura is a tree in the family Fagaceae. The specific epithet ' is from the Greek meaning 'few nerves', referring to the leaf venation.
Castanopsis oligoneura grows as a tree up to tall with a trunk diameter of up to . The brownish bark is smooth to lenticellate. The coriaceous leaves measure up to long. Its roundish nuts measure up to long.
Castanopsis oligoneura is endemic to Borneo. Its habitat is lowland dipterocarp forests up to elevation.