The essential oil of aerial parts from Baccharis obtusifolia (Asteraceae) growing wild in Ecuador was obtained by hydrodistillation and examined by gas chromatography�mass spectrometry (GC�MS and GC�flame ionization detector (GC�FID) analysis. Thirty-one individual compounds were identified and constitute 96.1% of the total composition of the oil. The main constituents of the oil were limonene (28.3%), germacrene-D (9.8%), ?-pinene (9.0%), ?-pinene (8.2%), bicyclogermacrene (6.2%) and ?-cadinene (5.7%). The essential oil showed significant antibacterial and antifungal activity. Baccharis obtusifolia oil exhibited a moderate antibacterial effect against Klebsiella pneumoniae (ATCC 9997) and Enterococcus faecalis (ATCC 29212), and good antifungal activity against Trichophyton rubrum (ATCC 28188) and Trichophyton mentagrophytes (ATCC 28185). In this study, the chemical composition and biological activity of the essential oil of B.�obtusifolia (Asteraceae) are reported for the first time.