Abstract: Commercial hot dip 5% Al-Zn alloy coated sheet steel was investigated for its corrosion behavior in three different seawater zones at Qingdao site with electrochemical measurement, weight loss test and SEM. The results indicated that in immersion zone 5% Al-Zn alloy coating resists well to the seawater corrosion because of its low current density and highly protective products from corrosion. In tidal zone the biofouling was found somewhat on coupons with oxidized surface resulting from quite good aeration, and the corrosion rate of the coating exposed in this zone is obviously lower than that in immersion zone. As to splash zone, 5% Al-Zn alloy coating shows the best corrosion resistance without biofouling found, which may be attributed to the advantageous aeration in combination with the corrosion resistant effect of the products from corrosion itself. A conclusion is therefore drawn that the corrosion resistance of 5% Al-Zn alloy coating increases by 197% and 183% in splash and tidal zones, respectively in comparison with that in immersion zone, and this coating tends to suffer from local corrosion in immersion and tidal zones.