The effects of different contents of Y on microstructures and corrosion resistances of Mg-5Al-1Sr-2Ca alloys were investigated. Mg-5Al-1Sr-2Ca-XY(X=0,0.5,0.7,1.0; wt%) alloys were prepared using mixture method and were analyzed by optical microscopy (OM), scanning electron microscopy(SEM) and X-ray diffraction (XRD). The results indicate that the grain size can be obviously reduced when the content of Y is 0.7 wt%. With the addition of Y, Al2Y phase is formed and acts as the heterogeneous nucleus of α-Mg to enhance the nucleation rate. Simultaneously, Al2Y is aggregated in the front of α-Mg and hinders the growth of α-Mg grains. The corrosion resistance of Mg-5Al-1Sr-2Ca-XY(X=0,0.5,0.7,1.0; wt%) alloys in 3.5% NaCl aqueous solution was investigated through static weight-loss test and polarization curve measurement. It is found that due to the addition of Y, the corrosion resistance is improved substantially. Mg-5Al-1Sr-2Ca-0.7Y alloy has a low corrosion current and the best corrosion resistance among the investigated alloys