Ageratum conyzoides is an erect, branching, soft, slightly aromatic, annual herb with shallow, fibrous roots. It grows to approximately 1 m in height. The stems and leaves are covered with fine white hairs; the leaves are egg-shaped with broad end at base (ovate) up to 7.5 cm long.
The flowers are purple, blue, pinkish or white, less than 6 mm across, with around 30 to 50 flowers and arranged in close terminal flower-heads. The fruits are small brown one-seeded achene fruits.