Conventional casting method was adopted to fabricate the alloys of Mg-Zn-Y, in which the dendritic morphology and its relation to the damping properties of as-cast Mg-Zn-Y alloy were studied based on the typical Mg93Zn6Y1 alloy containing icosahedral quasicrystal phase. By controlling the pouring temperature, the stirring speed and stirring time, the dendritic morphology with different parameters was obtained. The results show that the microstructure of the as-cast Mg93Zn6Y1 mainly consists of α-Mg dendritic crystal and icosahedral quasicrystal phase. After stirring, the primary α-Mg dendritic gradually have fractal characteristics in faith, and its size changes, affecting the damping capacity. The mechanism was discussed in detail.