Abstract: Commercial hot-dip 55% Al-Zn alloy coated sheet steel was investigated for its seawater corrosion behavior in Qingdao through electrochemical measurements, weight loss tests and SEM, where the coating was exposed to different seawater zones. The results indicated that the 55% Al-Zn coating is superior to conventionally galvanized coating and 5% Al-Zn coating in anticorrosivity when its specimens were immersed in seawater because of its low corrosion current density and protective corrosion products. Since the protective zinc corrosion products are mechanically retained in the Al-rich interdendritic network to retard further corrosive attack and the well-aerated condition promotes the passivity of the Al-rich phase so as to inhibit greatly the mass transfer process of corrosion, the 55% Al-Zn coating shows better anticorrosivity in tidal and splash zones than in immersion zone, i.e., 2-3 times as high as in immersion zone. What is worthy to notice is that serious pitting corrosion was found when the 55% Al-Zn coating specimens were in immersion zone.