Abstract Baccharis plants have been used since ancient times in American traditional medicine. Baccharis chilco is a perennial shrub of temperate regions of South America that grows well in rainfall forests of Colombia. Neither chemical composition nor biological studies of this plant have ever been reported. Two caffeoylquinic acid (CQA) derivatives, 5‐ O ‐[( E )‐caffeoyl]quinic acid ( 1 ) and 3,5‐di‐ O ‐[( E )‐caffeoyl]quinic acid ( 3 ), and rosmarinic acid ( 2 ) have been isolated from B. chilco growing wild in Colombia, using the on‐line HPLC‐DAD‐DPPH radical‐scavenging detection technique as guidance. In the course of the purification work, L ‐ chiro ‐inositol ( 4 ) was also isolated. Structures of the four isolated compounds were determined by spectroscopic methods. Antioxidants 2 and 3 exhibited high antiradical activities evaluated by the 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH . ) assay, although somewhat lower than that of the reference compound ascorbic acid. The on‐line HPLC‐DAD‐DPPH technique allowed a rapid pinpointing of antioxidants in the studied EtOH extract, and the facile guided isolation of the target molecules.