Objective: To identify the main chemical classes of compounds from aqueous extract of Enterolobium contortisiliquum (E. contortisiliquum) seed bark and to evaluate its anti-bacterial activity, as well as its potential to increase the activity of antibiotics against strains of Staphylococcus aureus,Pseudomonas aeruginosa and Escherichia coli. Methods: Different classes of compounds in the aqueous extract of E.contortisiliquum were evaluated based on the visual changes in the coloration and the formation of pre-cipitate after the addition of specific reagents.The antibacterial activity of the extract and its potential to increase of antibiotic activity of antibiotics drugs, gentamicin and nor-floxacin was determined by using the microdilution method. Results: Our results demonstrated that the following secondary metabolites were pre-sented in E. contortisiliquum seed bark: flavones, flavonols, xanthones, flavononols, chalcones, aurones,flavones and catechins. The extract itself had very low antibacterial activity against all bacterial strains tested (MIC ≥ 1 024 μg/mL), but there was an in-crease in the antibiotic activity of gentamicin and norfloxacin when combined in the sub-inhibitory concentration (i.e.,MIC/8). Conclusions: Our data suggests that E.contortisiliquum seed bark may be an altative source for new drugs with the potential to increase antibiotic activity against different strains of bacteria.