The leaf and root tip tissues of Alternanthera philoxeroides were treated with vulculic acid of different concentrations to study the effects of vulculic acid on the ultrastructure.The results showed that the damages appeared as the disruption of plasma membrane,digestion of the membrane of chloroplast and mitochondria,disorder of chloroplast lamellae,digestion of mitochondria ridge in leaf tissue,disruption of plasma membrane,digestion of mitochondria membrane and ridge,vacuolation and shrinking of meristematic and epidermal cells in root tip tissue.The severity of damages was increased with the increasing concentration of toxin and time of treatment.