Introduction: Fucoidan is a sulfated polysaccharide that has a wide range of bioactivities including anti-cancer. This polysaccharide commonly is extracted from marine brown seaweed. There is lack of information on the fucoidan extracted from tropical brown algae and its anti-cancer activity. Objectives: The objectives of this study were to purify fucoidan from Sargassum sp., Turbinaria sp. and Padina sp., and to evaluate their cytotoxicity against breast cancer (MCF-7) and colon cancer cells (WiDr). Materials and Methods: Fucoidan extraction was conducted by using acid extraction method. Purified fucoidans were obtained by DEAE cellulose column chromatography and confirmed by HPLC and FT-IR spectrometry. The cytotoxicity was evaluated by using the MTT (3-[4,5-dimethylthiazol-2-yl] -2,5- diphenyltetrazolium bromide) assay. Results: Fucoidan from Sargassum sp. and Turbinaria sp. showed low cytotoxicity with IC50 ranging between 461-663 μg/mL. Higher cytotoxicity against MCF-7 and WiDr was showed by fucoidan from Padina sp. with IC50 of 144 and 118 μg/mL, respectively. While its IC50 against Vero cells was 501 μg/mL.Standard fucoidan from Fucus vesiculosus exhibited IC50 of 60, 63 and 211 μg/mL against MCF-7, WiDr and Vero Cells, respectively. Although the IC50 was higher than that of standard fucoidan, Padina sp. fucoidan showed cytotoxicity comparable with standard fucoidan at concentrations below 100 μg/mL. Conclusion: These results indicated that Padina sp.fucoidan showed potential selective cytotoxicity, and promising for the development of an anti-cancer compound.