Corrosion behavior of pure Mg and Mg-Li Alloy in 3.5% NaCl solution of pH=7 was investigated through open circuit electrode potential vs time curve,polarization curve and impedance spectroscopy.The corrosion surface appearances were analysed by SEM,the surface components of pure Mg and Mg-Li alloy before and after corrosion were characterized by XRD,and the average corrosion velocity was detected by means of weight loss.The results indicated that pure Mg had less corrosion current,larger corrosion potential and electrochemistry reactive resistance than those of Mg-Li alloy in early stage of corrosion,but average corrosion velocity of pure Mg was larger than that of Mg-Li alloy after 24 h corrosion and the corrosion appearances were different.A few big and deep corrosion pits were formed on the surface of pure Mg,while the surface of Mg-Li alloy turned black and there were many little and shallow corrosion pits on it.The corrosion product on pure Mg surface was mainly Mg(OH)2,the corrosion products on Mg-Li alloy surface were consisted of Mg(OH)2,LiOH,MgLi,Mg3Li7,Al2O3.