Seven free-radical-scavenging phenolic compounds including five flavonoids, rutin (1), chrysoeriol 7-O-rutinoside (2), kaempferol 3-O-glucoside (3), chrysoeriol 7-O-glucoside (4) and naringenin (5), and two phenylethanoid glycosides, forsythoside B (6) and acteoside (7) were isolated from the methanol extract of the aerial parts of the Iranian medicinal plant Phlomis caucasica by reversed-phase preparative high-performance liquid chromatography (HPLC), and the structures of these compounds were elucidated by spectroscopic means. The free-radical-scavenging properties of 1–7 were assessed by 2,2-diphenyl-1-picryl hydrazyl (DPPH) assay. Among these compounds, forsythoside B (6) and acteoside (7) were found to be the most potent antioxidants with the RC₅₀ values of 4.97 and 4.27 μg/ml, respectively.