Abstract The essential oil and the MeOH extract of the leaves from Baccharis magellanica and B. elaeoides were found to be active against the bacteria Staphylococcus aureus. Analysis of the leaf essential oil yielded 0.3% v/w and 0.7% v/w, respectively. Analysis by GC-FID and GC/MS established the major constituents of both species. In B. elaeoides the major constituents were γ-cadinene (9.9%), limonene (9.1%), Ï-cadinol (8.4%), α-cadinol (8.1%), β-pinene (5.0%), β-patchoulene (4.9%), α-muurolene (4.0%), α-pinene (3.6%), α-calacorene (2.7%), γ-muurolene (2.7%), α-thujene (2.5%), α-cubebene (2.4%) and terpinen-4-ol (2.2%), and in B. magellanica the major constituents were 4-hydroxy- acetophenone (30.5%), massoia lactone (9.2%), α-cadinol (6.5%), γ-eudesmol (4.9%), elemol (3.7%), β-eudesmol (2.5%) and caryophyllene oxide (2.3%).