Mallotus pleiogynus is a species of plant in the family Euphorbiaceae. It is a tree that grows to tall and is native to New Guinea.
M. pleiogynus is native to the island of New Guinea, occurring in both Western New Guinea and Papua New Guinea. It is mostly found in primary forests, sometimes also secondary forests, at altitudes of up to . It prefers flat terrain.
M. pleiogynus is an evergreen tree growing up to tall, with a trunk diameter of up to . The outer bark is brown to grey in colour and smooth, with white to yellow inner bark. The papery leaves are ovate in shape with a pointed tip and rounded base, measuring by . There are 2-4 large, dark brown nectaries at the base of each leaf on the upper surface. The undersides of the leaves are densely hairy. M. pleiogynus is dioecious and the inflorescences are racemes, produced singly or less commonly in a pair. Male plants produce inflorescences up to long, with dark coloured flowers measuring in diameter and composed of 3-4 pointed sepals surrounding a cluster of 15-50 stamens. Female plants produce inflorescences up to long, each flower measuring in diameter and bearing 4-6 sepals and several plumose stigmas. The fruits are ellipsoid indehiscent drupes measuring by . The exterior of the fruit is hairy and somewhat wrinkled, yellow to orange when fresh when fresh, turning yellowish to reddish brown and developing 7-9 distinct longitudinal ridges when dry.