A novel numerical model capturing the evolution of cross-sectional microstructure to investigate its effect on corrosion behavior of magnesium (Mg) alloys is presented in this work using a moving mesh technique in COMSOL Multi-Physics (R). The model is capable of tracking the moving boundary of the corroding phase (alpha phase). The effect of beta phase fraction and its distribution on the corrosion behavior is addressed here assuming uniform Al content in the phase. The effects of beta phase fraction on corrosion behavior estimated from the model are validated with SVET experiments. A novel formulation using a level set function is used to study the effect of two representative microstructure configurations along the depth of the alloy: (a) continuous beta phase network around the a phase, and (b) discrete beta phase. The Mg alloy with a continuous beta phase network is found to display accelerated corrosion in the initial stage of exposure due to increasing beta phase fraction. However, corrosion tends to be halted after the a phase is preferentially dissolved and the continuous p phase network is exposed to electrolyte due to beta phase enrichment. (C)010 Elsevier Ltd. All rights reserved.