Castanopsis clemensii is a tree in the family Fagaceae. It is named for the American chaplain and plant collector Joseph Clemens.
Castanopsis clemensii grows as a tree up to tall with a trunk diameter of up to . The yellowish white bark is smooth or cracked or lenticellate. The coriaceous leaves measure up to long. Its ellipsoid nuts measure up to long.
Castanopsis clemensii is endemic to Borneo. Its habitat is lower forests to altitude.