Castanopsis megacarpa is a tree in the family Fagaceae. The specific epithet ' is from the Greek meaning 'large fruit'.
Castanopsis megacarpa grows as a tree up to tall with a trunk diameter of up to . The grey bark is smooth or slightly fissured. The coriaceous leaves measure up to long. Its roundish or ellipsoid nuts measure up to long.
Castanopsis megacarpa grows naturally in Thailand, Borneo, Peninsular Malaysia and Singapore. Its habitat is dipterocarp, kerangas or lower forests up to altitude.
The wood is locally used in making domestic items.