Mimosa pigra is a plant commonly used for medicinal purposes in the treatment of several diseases. However, studies regarding its toxicological properties are scarce. We evaluated the toxic, cytotoxic, genotoxic and mutagenic activities of leaf and stem infusions of M. pigra collected in the region of Delta do Parnaíba, Piauí, Brazil, through an in vivo Allium cepa test. Three concentrations of leaf and stem treatments were used (leaf treatment 1 and stem treatment 1 = 0.771 g/L; leaf treatment 2 and stem treatment 2 = 1.542 g/L; leaf treatment 3 and stem treatment 3 = 3.084 g/L), in addition to the negative controls (water) and positive controls (copper sulfate-1.2 mg/mL-A. cepa test). All the treatments were toxic, causing significant root growth inhibition. Leaf treatment 1, leaf treatment 3 and stem treatment 1 showed significant inhibition of the mitotic index. Leaf treatment 2, stem treatment 1 and stem treatment 3 showed significant genotoxic activity based on the frequency of chromosomal aberrations. The tested concentrations did not provoke significant mutagenic activity ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 19 (3): gmr18588 M.S. Araújo et al. 2 when compared to the negative control. We suggest that further studies with other biological systems are needed to evaluate the safetyness of M. pigra infusions for therapeutic purposes.