The electrochemical impedance measurements were carried out in a 3.5% NaCl solution for Crcoated plain carbon steels. Steels with two types of surface paintings containing polyesters and with or without an extra layer of aluminum tripolyphosphate were studied in this work. The variations of capacities and resistance verse immersion time were investigated. It has found that the capacity increased but the resistance decreased with increasing immersion time which indicates the degradation of coatinglayers. It is observed that the steel with an extra layer of aluminum tripolyphosphate has better corrosion resistance.