Cathodic delamination-weakening or loss of adhesion between the coating and the metal-is one of the major failure processes of organic coatings. Generally, it is almost inevitable to introduce defects to the coating during processing and operation. In this work, the delamination process of coatings around defects and the corrosion in defective coated metals was elucidated using immersion and electrochemical impedance tests. Two types of coatings (styrene-acrylic coating and terpolymer coating) were compared. The effects of defect size, chloride ion concentration and resin type on cathodic delamination were investigated. A small defect may affect the metal corrosion. Increasing the chloride ion concentration can promote the corrosion of metal but may not accelerate the delamination of the coating. The resin type is the key factor in the failure process of the coating.