This study described the isolation and structure elucidation of secondary metabolites from, Artimisia sieberi (Asteraceae), known for its therapeutic and medicinal properties, it was used in both traditional and modern medicine. Artimisia sieberi was collected at the flowering stage. Dried aerial parts were powdered and subjected to different chromatographic methods of extraction followed by different methods of purification through normal phase and reversed phase chromatography, eg. column chromatography (CC) and high performance liquid chromatography (HPLC), respectively. Phytochemical investigation of A. sieberi afforded a 3α,8β-dihydroxygermacr-4(15),9-dien-6α,7β,11αH,12,6-olide (1) and a flavonoid 3'-hydroxygenkwanin (2). The structures of the compounds were elucidated by means of spectroscopic analyses, including (EI-MS and 1D /2D NMR) techniques. Cytotoxic effects of these two known compounds were examined against, three different human cancer cell lines, MCF-7 (breast), HCT116 (colon) and HepG-2 (liver). Viability was assessed by the standard colorimetric assay using the tetrazolium, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and can be regarded as an potent source of lead compounds in drugs development to combat cancer.