The electrochemical corrosion behavior of an amorphous magnesium alloy （Mg58.5 Cu30.5 Y11 （at. % ））and its cast counterpart was investigated in 0. 005 mot/LH2SO4 ＋ 0. 25 mol/LNa2SO4 solutions using potentiodynamic measurement and scanning electron microscopy（SEM） and energy-dispersive X-ray （EDX）. The result showed that both amorphous and its cast counterpart exhibited active dissolution. Around open circuit potential, the amorphous alloy dissolved more quickly than the cast one owing to its higher reaction activity. However, when the anodic polarized up to certain value, Cu atoms would deposit on the surface of amorphous alloy and protected it from further corrosion. For the cast alloy, the dissolution rate was accelerated by galvanic processes between different phases.