Fucoidan, one kind of polysaccharides extracted from brown seaweeds, displays anti-proliferation and anti-metastasis activities in tumors.Here we found fucoidan inhibits MDA-MB-231 human breast cancer cells growth, decreases cell colony formation.In a xenografi-mice model, we demonstrated tumor volumes and metastatic lung nodules were reduced by fucoidan treatment in 4T1 breast cancer cells-bearing mice.The molecular network of TGFB receptors (TGFR) plays important roles in regulation of epithelial to mesenchymal transition (EMT) in cancer cells.