Mg-Zn-Zr-Y alloys containing quasicrystal phase were prepared by an as-cast method with water-cooling. On this base, the effects of different Zn and Y content (the same Zn/Y ratio) on microstructure and micro-hardness were also discussed. The results show that the increase of cooling rate by water-cooling can increase the volume fraction of quasicrystal phase (I-phase, Mg3YZn6) of Mg-Zn-Zr-Y alloy. The decreasing of grain sizes of the as-cast alloy is due to the increase of constitutional supercooling by Y addition. The solid solubility of Zn in α-Mg matrix mainly affects the hardness of the matrix, and the hardness of I-phase is much higher than that of the matrix. The liquidus temperature decreases substantially while the solid temperature does not change with Y addition, which weakens the hot cracking tendency of the ingot due to the decrease of freezing range.