Baccharis articulata is traditionally used as diuretic and digestive in local folk medicine of south of Brazil, Uruguay and Argentina. The antioxidant activity of crude ethanol and aqueous extracts, together with ethyl acetate and n-butanol fractions obtained from aqueous extract of B. articulata was determined using TRAP and TBARS assays. The n-butanol fraction was found to be the most active and its major compound (BaII) was isolated, identified and assayed. The structure of the phenolic compound BaII was established by means of spectroscopic and chemical methods as 4'-O-beta-D-glucopyranosyl-3',5'-dimethoxybenzyl-caffeate. This previously unreported metabolite presented similar antioxidant capacity when compared to Trolox.