The Mg97-xZn1Y2Gdx alloys were prepared by as-casting method. Corrosion performance of alloys was evaluated by using potentiodynamic polarization, hydrogen evolution rate and mass loss measurements in 3% sodium chloride solution at room temperature. The results shown that the atomic rate of the long period stacking ordered (LPSO) with the composition of Mg12Zn1Y1. The microstructure of LPSO phases was lamellar structure. When the atomic fraction of Zn is 1% and the atomic ratio of Zn/RE (Y, Gd) is 2:5, the volume fraction of LPSO phase can reach the extreme value. The corrosion resistance of Mg–Zn–Y alloy improves with the increase of the volume fraction of LSPO phase. The Mg96.5Zn1Y2Gd0.5 (MG0.5) alloy had better corrosion resistance than those of other alloys. It meant that 0.5 at. % gadolinium (Gd) was a suitable addition to Mg97Zn2Y alloy about corrosion resistance