Abstract 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 ® . The model is capable of tracking the moving boundary of the corroding phase (α phase). The effect of β phase fraction and its distribution on the corrosion behavior is addressed here assuming uniform Al content in the α phase. The effects of β 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 β phase network around the α phase, and (b) discrete β phase. The Mg alloy with a continuous β phase network is found to display accelerated corrosion in the initial stage of exposure due to increasing β phase fraction. However, corrosion tends to be halted after the α phase is preferentially dissolved and the continuous β phase network is exposed to electrolyte due to β phase enrichment.