Currently the challenges faced in medicine are investigating an anticancer drug that destroys tumor cells in the presence of normal cells without undue toxicity. Marine components such as seaweeds which exhibit antitumor activity are enlisted in the literature which has emphasized its potential implications. This Study is conducted to screen the antitumor effect of Brown and Red seaweed namely Sargassum sp, and Corallina sp. Isolated from Sindhudurg west coast from Maharashtra against MDA-MB-231 (Triple negative Breast Cancer) cell line. Ethanolic extract of both the marine seaweed was concentrated using a Soxhlet apparatus and its aqueous form is used for further evaluation.MTT assay (3-(4, 5-dimethylthiazol-2-yl)-2, 5- diphenyltetrazolium bromide, a yellow tetrazole) was performed for In vitro assessment of cytotoxic activity of Sargassum sp. at various concentrations (25 µg/ml-400 µg/ml) against the chosen cell lines. Investigation documented cell viability percentage, have been reduced with increased concentration, as evidenced by cell death. The marine extract showed significant potential cytotoxic activity (P<0.001) and (P<0.05) with IC50 of 28.01 µg/ml and 27.43 µg/ml respectively, against MDA-MB 231cell line. Anti- tumor effect of the ethanolic extract of Sargassum sp induced cell apoptosis with evidence of bioactive components. The successful application of Sargassum sp as a potent therapeutic tool against cancer need to be explore through further research.