Phytochemical Investigation of the leaves of Artemisia sieberi growing in Saudi arabia leads to isolation of eight sesquiterpene lactones of eudesmanolide 1-4, germacranolide 5-7 and davanone 8 types in addition to six methoxylated flavonoid derivatives 9-14. The structures of the isolated compounds were elucidated on the basis of spectroscopic evidences and correlated with known compounds. The cytotoxic activity of the isolated compounds was evaluated against human Hela and MCF-7 cell lines. The results exhibited that none of the isolated sesquiterpenoids displaying any cytotoxic activity whilst isolated flavonoids exhibited promising growth inhibitory action.