The leaves of three Ligularia species belonging to the family Compositae, Ligularia stenocephala, L. fischeri, and L. fischeri var. spiciformis, were qualitatively and quantitatively analyzed on the caffeoylquinic acids by HPLC and subjected to peroxynitrite-scavenging assay. The IC(50) of the MeOH extract of L. stenocephala was 1.62+/-0.03 mug/ml and the major caffeoylquinic acids of L. stenocephala were 5-O-caffeoylquinic acid, 3,5-di-O-caffeoyl-muco-quinic acid, and 3,5-di-O-caffeoylquinic acid. The compositions of caffeoylquinic acids were different for the three plants. Since percentage of total caffeoylquinic acids of the extract was highest (42.20% of the MeOH extract and 94.52% of the BuOH extract) in L. stenocephala and potent in peroxynitrite-scavenging assay, the extracts of L. stenocephala were chosen to perform in vivo anti-ulcerogenic activity. Treatment of mice with the MeOH- and BuOH extracts decreased the diameter of gastric lesions caused by HCl/ethanol- and indomethacin/bethanechol and decreased the volume of gastric juice, suggesting that caffeoylquinic acids have anti-ulcerogenic activity. These results suggest that the leaves of Ligularia species may help prevent or treat gastric ulcers.