The corrosion performance of new creep resistant magnesium-rare earth alloys was studied and related to its microstructure and chemical composition. The commercial alloy MEZ™ was used as reference. The alloys were produced by the Squeeze Cast Technique. Corrosion was studied in two media: ASTM Water (mild medium) and in 3.5% NaCl at pH 11 (strong medium) by measuring electrochemical polarization curves and by examination of the pitting morphology. Mg-Al-RE alloys had the best corrosion resistance in mild medium. In the aggressive medium, the reference alloy with high RE-content was the best, followed by the Mg-Al-RE alloys. High ratios of Fe/Mn were found detrimental for the corrosion properties of the alloys, especially in strong media. The microstructure played an important role: the eutectic phases of the alloys were cathodic to the matrix and acted as barriers against the propagation of the pitting corrosion. Filiform corrosion was observed additionally in the Mg-Al-RE alloys.