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 1β,4β-dihydroxyeudesman-11-ene; 1β,7α-dihydroxyeudesman-4(15)-ene; (1R,5S,6S,7S,10R)-1β, 6α-dihydroxyeudesman-4-one and 1β-D-glucopyranosyloxy-6α-hydroxyeudesman-4(15)-ene. In addition, a chemical transformation of a known compound 1β,6α-dihydroxy-eudesman-4 (15)-ene was carried out and the derivative 1β,6α-dihydroxy-4β(15)-epoxyeudesmane was obtained. Some of the compounds were evaluated for their in vitro antitumor activities.