The effect of ozone on corrosion of mild steel in flowing seawater was investigated by using immersion test and electrochemical techniques including potentiodynamic polarization and electrochemical impedance spectroscopy. It is found that the weight loss of the steel specimens in the seawater containing 2 ppm ozone is significantly less than that in natural seawater. Localized corrosion occurs in the specimens exposed to ozonated seawater, while general corrosion happens to the specimens in natural seawater. Ozone facilitates the formation of corrosion-protective film on steel surface, which increases the charge transfer resistance and decreases the anodic current of steel in seawater. (C) 2011 Elsevier Ltd. All rights reserved.