The corrosion of a magnesium alloy containing rare earth elements (WE43 type alloy) was studied in 0.05 and 0.5 M Na2SO4 or 0.1 and 1 M NaCl solutions using electrochemical techniques: linear polarization resistance, potentiodynamic polarization, impedance measurements. The electrolytes favoured anodic magnesium oxidation but the presence of rare earth elements improved the tendency of magnesium to passivation. The dissolution rates in chlorides were higher than in sulphates because chlorides, in contrast to sulphates, interfered with the formation and maintenance of a protective layer of corrosion products which decreased the severity of the attack. The effects of galvanic corrosion due to cathodic intermetallic precipitates at grain boundaries were particularly evident in chloride media at long testing times.