INTRODUCTION AND OBJECTIVES: Breast cancer is the second most common type of cancer in the world. Chemotherapy may be the first modality in the treatment of a primary breast tumor and are usually performed with a combination of drugs. However, chemotherapy drugs do not only act on cancer cells, but also on normal cells. This process results in the known side effects of these medications. Natural products are potential sources of novel active molecules that may provide structural template for drug discovery. Bonnetia sp. belonging to the order Malpighiales, a large order of flowering plants that includes 40 families, more than 700 genera and approximately 16.000 species. Studies show that different species within Malpighiales present biological activities, such as antineoplastic, antimicrobial and anti-inflammatory effects. The aim of this study was to investigate the effect of crude extract of fruits of Bonnetia sp. in MDA-MB-231, MCF-7 and 4T1 breast cancer cells. MATERIAL AND METHODS: The viability of MDA-MB-231, MCF-7 and 4T1 cells strain were evaluated by MTT method. The phases of the cell cycle were analyzed in flow cytometry after labeling with RNAse-PI and by the production of reactive oxygen species by flow cytometry after labeling with the DCFDA. RESULTS AND CONCLUSION: Our results demonstrated that the crude extract of Bonnetia sp. fruits after treatment (25, 50, 75, 100 and 200 μg/mL) showed cytotoxicity in MDA-MB-231 and MCF-7 cells at 24 and 48 hours with IC50 of 170.40, 66.77, 115.00 and 177.10 μg/mL, respectively, and in 4T1 cells at 24 and 48 hours with IC50 of 139.20 and 95.30 μg/mL, respectively. The Bonnetia sp. extract increase 16.53-fold the sub-G0/G1 phases of cell cycle after 24 hours of treatment in MDA-MB-231 and decrease 13.58 and increase 17.27-fold the G0/G1 and S phases, respectively, in MCF-7 after 24 hours of treatment. The Bonnetia sp. decrease 38.54-fold the production of reactive oxygen species in MDA-MB-231 cells. In conclusion, our results demonstrated the cytotoxic effect of the crude extract of the fruit of Bonnetia sp. on breast cancer cells, which leads us to suggest it as a candidate for sources of new anti-cancer molecules.