Cytotoxicity-guided fractionation of the methanol soluble part of the dichloromethane extract of the leaves of Warionia saharae led to the isolation of the two new guaianolide-type sesquiterpene lactones, 5 alpha H-3 beta,4 beta-epoxy-14-oxo-guaia-1(10),11(13)-dien-6 alpha,12-olide (1), 5 alpha H-2 beta,4 beta-epoxy-3 alpha-hydroxy-guaia-1(10),11(13)-dien-6 alpha,12-olide (6), and the new eudesmane type sesquiterpene 1 beta,6 alpha-dihydroxycostic acid ( 4). In addition, the known sesquiterpene lactones 5 alpha H-2 beta-hydroxyguaia-3(4),10(14),11(13)-trien-6 alpha,12-olide (2), reynosin (3), 5 alpha H-1 alpha,10 alpha:3 alpha,4 alpha-diepoxyguaia-11(13)-en-6 alpha,12-olide (5), and dehydroleucodin (7) were isolated together with the known flavone hispidulin. Cytotoxicity testing of the sesquiterpene lactones against the KB cancer cell line (ATCC CCL17) revealed IC50 values of 3.5 (1), 2.6 ( 2), 2.7 ( 3), 4.3 ( 5), 3.6 ( 6), and 1.3 (7) microg/mL. Compound 4 was not active up to 20 microg/mL.