The corrosion mechanism of magnesium has been the subject of several papers, aiming to explain all the reported phenomena occurring at the Mg/electrolyte interface in general, and the negative difference effect (NDE) particularly [1]. In fact, this phenomenon consists on an increase of the hydrogen evolution rate with anodic polarization [2]. On this aspect, many mechanisms have been proposed including the uni-positive Mg+ ion mechanism [3], the magnesium hydride (MgH2) model [4], the partially protective surface film model [5], the incomplete film univalent Mg+ ion mechanism [6], the adsorptive univalent Mg+ ion dissolution model [7], and the Mg*H/Mg*OH catalysts model [8]. In this work, the pH effect on the corrosion of magnesium, at the early stages, was investigated using electrochemical impedance spectroscopy (EIS). A special attention has been paid to the low frequency (LF) inductive loops. Indeed, it is shown that depending on the pH value in acidic solution, one or two inductive time-constant can be observed (Fig. 1). On the basis of the obtained results, a model was established in view of understanding the elementary steps involved in the Mg corrosion mechanism and the impact of the pH on the kinetics of the different reactions. Interestingly, it is shown that a single mechanism can describe the corrosion behavior in the acidic to slightly alkaline pH domain (1.8 – 7.7) and that the presence of multiple LF time-constants is also to be linked to the thin oxide film present on the Mg surface. [1] J. Huang, G.-L. Song, A. Atrens, M. Dargusch, What activates the Mg surface—A comparison of Mg dissolution mechanisms, J. Mater. Sci. Technol. 57 (2020) 204–220. [2] W. Beetz, On the development of hydrogen from the anode, Lond. Edinb. Dublin Philos. Mag. J. Sci. 32 (1866) 269–278. [3] J.W. Turrentine, Reversed Electrolysis, J. Phys. Chem. 12 (1908) 448–467. [4] G.G. Perrault, Potentiostatic study of the magnesium electrode in aqueous solution, J. Electroanal. Chem. 27 (1970) 47-58. [5] G. Song, A. Atrens, D. Stjohn, J. Nairn, Y. Li, The electrochemical corrosion of pure magnesium in 1 N NaCl, Corros. Sci. 39 (1997) 855–875. [6] G.L. Song, A. Atrens, Corrosion Mechanisms of Magnesium Alloys, Adv. Eng. Mater. 1 (1999) 11-33. [7] G. Baril, G. Galicia, C. Deslouis, N. Pébère, B. Tribollet, V. Vivier, An Impedance Investigation of the Mechanism of Pure Magnesium Corrosion in Sodium Sulfate Solutions, J. Electrochem. Soc. 154 (2007) C108-C113. [8] C.D. Taylor, A First-Principles Surface Reaction Kinetic Model for Hydrogen Evolution under Cathodic and Anodic Conditions on Magnesium, J. Electrochem. Soc. 163 (2016) C602–C608.