The present study was to investigate the protective effect of Echinacea, purpurea (E. purpurea) extract, a natural scavenger of peroxynitrite (ONOO-), on the biomolecules injury induced by ONOO- in vitro. The results showed that E. purpurea extract could prevent the ONOO--mediated damage in tyrosine nitration, low density lipoprotein (LDL) oxidation and DNA strand breaks. The ONOO- scavenging ability of E. purpurea in the process of 3-nitrotyrosine (3-NT) formation exhibited dose-dependent manner. The results of LDL oxidation assay indicated that the extract could inhibit LDL oxidation correlates with lipid hydroperoxide concentration. In addition, E. purpurea was able to inhibit ONOO'-induced DNA damage by 50% at a concentration of 150 mug/ml. For further study on the relationship of scavenging activity between the complex and the monomer, we isolated a unique component from E. purpurea, cichoric acid as an active constituent, which has stronger inhibition effects against ONOO--induced tyrosine nitration and DNA single strand breaks.