Xanthophyllum pachycarpon is a tree in the family Polygalaceae. The specific epithet ' is from the Greek meaning 'thick fruit', referring to the thick wall of the fruit.
Xanthophyllum pachycarpon grows up to tall with a trunk diameter of up to . The smooth bark is greyish or dark green. The light brown fruits are round and measure up to in diameter.
Xanthophyllum pachycarpon is endemic to Borneo. Its habitat is mixed dipterocarp forests from sea-level to altitude.