The essential oil of the aerial parts of Baccharis grisebachii was examined by GC and GC-MS and evaluated for its antimicrobial properties. Forty three essential oil constituents were identified representing 94.3% of the total. Thymol, thymol methyl ether, thymyl acetate, alpha pinene, alpha humulene, and globulol were found to be the major components. The oil showed MIC values < 250 &#956;g/mL against Cryptococcus neoformans (125 &#956;g/mL), Aspergillus spp. (125 &#956;g/mL), and particulary against Trichophyton mentagrophytes and T. rubrum (62.5 &#956;g/mL)