The EtOAc and n-BuOH soluble fractions from the aerial part of Setaria viridis showed a strong free radical scavenging activity. Six major compounds were isolated from these fractions. They were identified by spectral data as tricin (1), p-hydroxycinnamic acid (2), vitexin 2"-Ο-xyloside (3), orientin 2"-Ο-xyloside (4), $tricin-7-Ο-{eta}-D-glucoside$ (5) and vitexin 2"-Ο-glucoside (6). Among these compounds, 4 and 5 exhibited strong free radical scavenging activities on 1, 1-diphenyl-2-picrylhydrazyl (DPPH). We further studied the effects of these isolated compounds on the lipid peroxidation in rat liver microsomes induced by non-enzymatic method. As expected, 4 and 5 exhibited significant inhibition on $ascorbic/Fe^{2-}$ induced lipid peroxidation in rat liver microsomes.ver microsomes.