Crude extracts of 45 medicinal plants from CPQBA Germoplasm Collection were tested for their antimicrobial activity. The species that presented strong activity (Minimal Inhibitory Concentration until 0.5 mg.mL-1) against the respective microorganisms were: Achillea millefolium (0.5), Mikania laevigata (0.04), Solidago chilensis (0.1), Piper marginatum (0.2) against Staphylococcus aureus; Aloysia gratissima (0.1), P. marginatum (0.2), M. laevigata (0.09) against Bacillus subtilis and Mentha pullegium (0.3), Mikania glomerata (0.1), M. laevigata (0.04), Stachytarpeta cayenensis (0.2) and Bacharis dracunculifolia (0.5) against Streptococcus faecium. According to results, M. laevigata was able to inhibit three bacteria species, at similar concentrations as observed for the standard chloranphenicol.