Castanopsis oviformis is a tree in the family Fagaceae. The specific epithet oviformis means 'egg-shaped', referring to the cupule.
Castanopsis oviformis grows as a tree up to tall with a trunk diameter of up to . The brownish bark is scaly or cracked. The coriaceous leaves measure up to long. Its ovoid nuts measure up to long and are considered edible.
Castanopsis oviformis is endemic to Borneo. Its habitat is hill dipterocarp and kerangas forests up to elevation.