Mastixia macrocarpa is a tree in the family Nyssaceae. The specific epithet ' is from the Greek meaning "large fruit".
Mastixia macrocarpa grows as a tree measuring up to tall with a trunk diameter of up to . The pale green fruits are oblong- and measure up to long.
Mastixia macrocarpa grows naturally in Malaysia's Sarawak state and the Philippines' Luzon island. Its habitat is mixed dipterocarp forests at around altitude.