The chemical composition of the essential oil from Lantana montevidensis Briq. and its antibiotic resistance modifying activity were investigated by gas chromatography/mass spectrometry (GC/MS) and microdilution assay, respectively. β-Caryophyllene (31.50%), germacrene D (27.50%) and bicyclogermacrene (13.93%) were the main constituents. The essential oil was examined for antibiotic activity alone in association with aminoglycosides against Escherichia coli Ec27 and Staphylococcus aureus Sa358. The results showed antibacterial activities of the oil and synergistic effects combined with aminoglycosides. The most expressive effect was the potentiating of amikacin on E. coli with minimal inhibitory concentration decrease (512-5 µg mL(-1)). The data obtained are indicative of the antibacterial activity of the essential oil of L. montevidensis and its potential in modifying the resistance of aminoglycosides analysed.