Abstract:The effects of the decoction of Erythrina velutina Willd., Fabaceae, were investigated using the root meristem cells of Allium cepa L., Amaryllidaceae. Ten concentrations of the aqueous extract (0.125 to 1.25%) of this medicinal plant were analyzed at both macroscopic and microscopic levels. All concentrations showed root growth inhibition after 96 h treatment. Although there were no signifi cant differences between the mitotic indexes of any concentration and the control, there were changes in the frequencies of cell stages at three different concentrations. Additionally, the presence of fi ve different cells abnormalities was recorded: chromosome bridging, lagging chromosomes, chromosome fragments, disturbed metaphase and disturbed anaphase. These results suggest inhibitory and genotoxic activity of the decoction of E. velutina on Allium cepa.