Research on corrosion behaviour of zinc in natural seawater without and with fucoidan was carried out by potentiodynamic polarization test and electrochemical impedance spectroscopy(EIS).The results revealed that fucoidan serves as a good inhibitor for zinc in seawater.Polarization curves suggested that corrosion potential values shifted to the positive ones after adding inhibitor and fucoidan retards anodic reaction more.Thus,fucoidan acted as anodic inhibitor.EIS results showed two phenomena including a charge-transfer and an adsorption film.The corrosion inhibition of fucoidan was further confirmed by the scanning electron microscope(SEM)and atomic force microscope(AFM)analysis.Langmuir's adsorption isotherm was found the appropriate adsorption model.