Four new and five known eudesmane-type sesquiterpenes were isolated from the aerial parts of Erigeron annus. The structures of these new compounds were elucidated by spectral means, including 2D-NMR analysis, to be 1 beta,4 beta-dihydroxyeudesman-11-ene; 1 beta,7 alpha-dihydroxyeudesman-4(15)-ene; (1 R,5 S,6 S,7 S,10 R)-1 beta, 6 alpha-dihydroxyeudesman-4-one and 1 beta- D-glucopyranosyloxy-6 alpha-hydroxyeudesman-4(15)-ene. In addition, a chemical transformation of a known compound 1 beta,6 alpha-dihydroxy-eudesman-4 (15)-ene was carried out and the derivative 1beta,6alpha-dihydroxy-4beta(15)-epoxyeudesmane was obtained. Some of the compounds were evaluated for their in vitro antitumor activities.