Four new pyrrolizidine alkaloids, ligularidine, neoligularidine, ligularizine and ligularinine, were isolated together with the known compound clivorine from the roots and aerial parts of Ligularia dentata. Their structures were elucidated on the basis of the spectral data and chemical conversion of clivorine into these alkaloids. A useful epoxidation of pyrrolizidine alkaloids was achieved by using performic acid. © 1984, The Pharmaceutical Society of Japan. All rights reserved.