Degradation of steels due to the hydrogen embrittlement, which is related to the hydrogen penetration reaction (HPR) into steel, is a serious problem from the standpoint of infrastructure preservation. A Devanathan-Stachurski permeation technique [1, 2] is a well-known method to determine a hydrogen penetration rate in metals. In this technique, two independent electrochemical cells are arranged on right across two surfaces of thin metal sheet and anodic and cathodic polarizations can be performed with each cell using the three-electrode system. The hydrogen penetration rate can be evaluated by measuring the oxidation current of hydrogen atoms diffused in the metal sheet at the anode side. The electrochemical impedance spectroscopy (EIS) was used for electrochemical measurement with the Devanathan cell to investigate HPR mechanisms because the time constants of hydrogen evolution and entry can be discriminated [3-5]. In this study, we used a complex hydrogen penetration ratio (CHPR), which is a transfer function related to hydrogen entry and diffusion in metal sheet, with the Devanathan cell to investigate kinetics of hydrogen entry into metals. The CHPRs of carbon steel sheet immersed in aqueous solution of different pH’s were measured in this study. The rate constant of hydrogen entry was determined by comparing experimental results with the simulated ones according to the theoretical equation, and influence of pH on hydrogen entry was discussed.