Research on corrosion behaviour of zinc in natural sea water without and with fucoidan was carried out by potentiodynamic polarisation test and electrochemical impedance spectroscopy(EIS). The results revealed that fucoidan serves as a good inhibitor for zinc in sea water. Polarisation curves suggested that corrosion potential values shifted to the positive ones after adding inhibitor and fucoidan retards anodic reaction more. Thus, fucoidan can be 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. Research on corrosion behavior of zinc in natural sea water without and with fucoidan was carried out by potentiodynamic polarisation test and electrochemical impedance spectroscopy (EIS). The results revealed that fucoidan serves as a good inhibitor for zinc in sea water. Polarisation curves suggested that corrosion potential values ​​shifted to the positive ones after adding inhibitor and fucoidan retards anodic reaction. 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.