Three new sesquiterpene lactones, 11alpha,13-dihydroxydehidrocostuslactone (1), the unusual 5, 10-epoxygermacranolide 4,15-anhydrohelivypolide (2), and 3-methoxy-1,2-anhydridoniveusin A (4), together with the 5,10-epoxygermacranolide helivypolide, four known 3,10-furanoheliangolides, and five known kaurane- and trachylobane-type diterpenes, have been isolated from Helianthus petiolaris.