A new electrochemical method for the scab corrosion test has been developed. Cathodic peak current density in multi-cyclic voltammetry can evaluate scab corrosion resistance of zinc phosphate coatings. A good correlation is obtained between the cathodic peak current density and the scab blister width in out-door exposure test. This peak current density is related to the oxygen reduction current density and the reduction current density of ferrous ions dissolved from the surface of phosphated steel. Accordingly, the cathodic peak current density is valuable for reproducible and rapid scab corrosion testing of zinc phosphate coatings.