Abstract: Astronium fraxinifolium is an arboreal species found throughout the Brazilian Cerrado region and used in folk medicine as antimicrobial, anti-hemorrhagic and healing. Pro-oxidant activity of extracts of A. fraxinifolium through Relative Electrophoresis Mobility (REM) of Bovine Serum Albumin (BSA) protein in presence of the extract and Cu2+ and also the genotoxic potential through Somatic Mutation and Recombination Test (SMART) and Allium cepa tests has been investigated during this study. In the REM, the extracts acting exclusively on BSA resulted in a band formation with higher molecular weight than BSA, probably due to oxidative action of the extracts. In presence of Cu2+ and extracts occurred protein fragmentation due to Cu2+ oxidative action potentiated by the extracts. In SMART test the frequency of mutant spots increases with the increased concentration of extract A. fraxinifolium (50 mg mL–1 = 1.40 and 100 mg mL–1 = 2.66). The HB cross shows a decrease in the total of mutant spots frequency for the different treatments (50 mg mL–1 = 6.60 and 100 mg mL–1 = 3.25). Evaluation of A. cepa test demonstrated the following results (concentration extract = chromosomal abnormalities) 1 mg mL–1 = 85, 10 mg L–1 = 61 50 mg mL–1 = 53, 100 mg mL–1 =33 and MMS 10 mg L–1 = 50. Genotoxic and cytotoxic actions can be explained by the actions of tannins present in its composition. But there may be other substances that also act for such results. The genotoxicity in medicinal plants contributes to therapeutic safety warning that although the use of medicinal plants is an inexpensive and non-aggressive method it can cause harmful effects if used incorrectly.