Zinc corrosion under 0.2 M NaCl solution films 5-800 mu m in thickness was studied by electrochemical impedance spectroscopy (EIS). As-polished and rusted zinc plates obtained by exposure to a natural atmospheric environment for 1, 3, 6, and 12 months were used as working electrodes. The obtained EIS results were analyzed using a transmission line equivalent circuit to determine the charge transfer resistance (R-ct), the reciprocal of which is proportional to the corrosion current density. For the as-polished zinc, the corrosion behavior is divided into three regions by the solution film thickness (X-f). In Region I (X-f: 800-200 mu m), R-ct(-1) is independent of X-f and is approximately ten times smaller than that for carbon steel. In Region II (X-f : 200-25 mu m), however, R-ct(-1) increases with decreasing solution thickness down to approximately 25 mu m due to an enhancement of the oxygen diffusion (cathodic process) through the solution film. In Region III (X-f < 25 mu m), further decreases in thickness reduce R-ct(-1) because the zinc dissolution (anodic process) is suppressed. In contrast, R-ct(-1) of the rusted zinc is independent of X-f because the charge transfer process is strongly suppressed by the zinc corrosion products, which were identified as simonkolleite and zinc oxide. (C) 2018 The Electrochemical Society.