Rare earth chemical conversion coating of Mg alloys was studied. Corrosion and electrochemical behavior in chloride environment were investigated with tests of evolution of hydrogen and electrochemical measurements. The surface morphologies and composition of rare earth conversion coating were studied through SEM, EDAX and XPS. The results showed that rare earth conversion coatings could improve corrosion resistance and their corrosion resistance was comparable with that of chromate coatings (HB/Z5078278). This result was further proved by Polarization and EIS.