Secondary metabolites of Tanacetum alyssifolium (Bornm.) Grierson (Asteraceae) were investigated for the first time. Thirteen compounds including axillarin (1), Luteolin-7-O-β-glucoside (8) and rutin (13) as flavonoids, fraxetin (7), isofraxidin (9), isofraxidin-7-O-glucoside (11) and fraxidin (12) as coumarins, tatridin A (2), altissin (3), tamirin (4) and tanachin (5) as sesquiterpene lactones and 2,4-dihydroxy-6-methoxy acetophenone (6) and picein (10) as acetophenone derivatives were isolated from the methanol extract of the species. The structures of all isolated compounds were elucidated by 1D and 2D-NMR techniques and by comparing with the literature data. In addition, in vitro cytotoxic activity of all isolated compounds was evaluated against breast cancer MCF-7 cell line by XTT assay. Sesquiterpene lactones; tatridin A (2), tamirin (4) and tanachin (5) were found to be the most cytotoxic molecules against MCF-7 cell line.