From Byrsonima crassifolia (L.) H.B.K. a tropical tree widely distributed in Mexico, Central and South America, which has been used medicinally since prehispanic times, we report here the antibacterial activities of organic extracts of roots and stems. The ethyl acetate of roots was the most active against Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi, Shigella flexneri, Staphylococcus aureus, Staphylococcus epididermis, Streptococcus pneumoniae and Micrococcus luteus.