Plants from the genus Centaurea (C.) (Family: Asteraceae alt. Compositae), widely distributed inAsia, Europe and North America, have traditionally been used in the treatment of variousailments. As a part of our on-going studies on the plants from the genus C. for theirphytochemistry and biological activities, extracts of the seeds of Turkish endemic C. species, C.bornmuelleri and C. huber-morathii, were tested for their cytotoxicity towards the CaCo2 coloncancer cell line as well as for the toxicity towards the brine shrimps, using the MTT and the brineshrimp lethality assays, respectively. Among the extracts, the MeOH extract of these plantsshowed significant toxicity towards the brine shrimps (LD50 = 55.2×10-2 and 42.4×10-2 mg/ml,respectively). The MeOH extract of both C. species also inhibited the growth of CaCo2 coloncancer cells in the MTT assay (IC50=29.9 and 33.0 g/ml, respectively). As the most prominentactivities in both assays were observed with the MeOH extracts, it can be assumed that thecompound(s) responsible for these activities are polar in nature.