The effect of the frequency of the pulsed magnetic field on Mg-Gd-Y-Zr alloy during solidification was investigated. When the pulsed magnetic field is applied to Mg-Gd-Y-Zr alloy during the solidification process, the grain refinement is achieved. The average grain size of the as-cast Mg-Gd-Y-Zr alloy is from 65 mm without the pulsed magnetic filed to 37 mm with the pulsed magnetic field of 5 Hz. Grain refinement of Mg-Gd-Y-Zr alloy is due to the electromagnetic undercooling and reduction of temperature gradient by the vibration of melt resulted from the pulsed magnetic field. Compared those casting method with traditional one, the tensile strength and elongation are increased by 4.8% and 78.5%, respectively