Abstract: 3.5% NaCl (mass fraction) aqueous solution as corrosion medium was dropped onto the surfaces of low-carbon ferritic steel, 09CuPCrNi steel and low-carbon bainitic steel to form thin liquid films. Initial corrosion of the steels was observed by metallographic microscope. Selected attack along grain boundaries occurred in both low-carbon ferritic steel and 09CuPCrNi steel, while this did not occur in low-carbon bainitic steel. The electrochemical impedance spectrum and polarization curve of the steel matrixes indicate that low-carbon bainitic steel exhibits the highest polarization resistance and the lowest corrosion current, so the initial corrosion rate of fine crystalline low-carbon bainitic steel was lower than that of the other two steels.