The extract of Artemisia asiatica herb with antiproliferative activity against four human tumor cell lines (A2780, A431, HeLa, and MCF7) was analyzed by the MTT assay, and bioassay-directed fractionation was carried out in order to identify the compounds responsible for the cytotoxic activity. Guaianolide (1-4), seco-guianolide (5), germacranolide (6) and eudesmanolide sesquiterpenes (7), monoterpenes (8, 9), including the new compound artemisia alcohol glucoside (8), and flavonoids (10-16) were isolated as a result of a multistep chromatographic procedure (CC, CPC, PLC, and gel filtration). The compounds were identified by means of UV, MS, and NMR spectroscopy, including (1)H-and (13)C-NMR, (1)H-(1)H COSY, NOESY, HSQC, and HMBC experiments. The isolated compounds 1-16 were evaluated for their tumor cell growth-inhibitory activities on a panel of four adherent cancer cell lines, and different types of secondary metabolites were found to be responsible for the cytotoxic effects of the extract. Especially cirsilineol (13), 3β-chloro-4α,10α-dihydroxy-1α,2α-epoxy-5α,7αH-guai-11(13)-en-12,6α-olide (3), and iso-seco-tanapartholide 3-O-methyl ester (5) exerted marked cytotoxic effects against the investigated cell lines, while jaceosidin (12), 6-methoxytricin (15), artecanin (2), and 5,7,4',5'-tetrahydroxy-6,3'-dimethoxyflavone (14) were moderately active. All the sesquiterpenes and monoterpenes are reported here for the first time from this species, and in the case of artecanin (2), 3α-chloro-4β,10α-dihydroxy-1β,2β-epoxy-5α,7αH-guai-11(13)-en-12,6α-olide (4), ridentin (6), and ridentin B (7), previously unreported NMR spectroscopic data were determined.