Eupatorium japonicum is a herbaceous perennial growing 50–200 cm tall from short rhizomes with many fibrous roots.

The leaves are oppositely arranged on the stems and have short but rather thick petioles that are 1–2 cm long.

The Leaves gradually tapper to a sharp point and the bases are broad or narrow, and the leaf margins are sometimes 3-partite.

The fruits are black-brown, 5-angled, hairless achenes, that are elliptic in shape and about 3.5 mm long, and are covered with yellow glands.

[3] King and Robinson, in a 1987 paper, considered E. japonicum to be part of a more broadly defined E.