Mg-3Al-xSr (x=0.1~0.9 wt%) alloys were prepared by a traditional cast method. Microstructures, electrical conductivities and micro-hardness of the present alloys in as-cast and as-heat treated states were studied by means of optical microscope, SEM, XRD, electrical conductivity meter and micro-hardness measuring instruments. The results show that Al4Sr phase is formed with little addition of Sr (<0.1 wt%). With increasing content of Sr, the electrical conductivity of as-cast Mg-Al-Sr alloys increases, and Mg-Al-Sr ternary phase (τ phase) is formed. After high temperature heat treatment at 400 oC, τ phase would decompose to Al4Sr phase, and the corresponding electrical conductivity of Mg-Al-Sr alloys increases with the heating time increasing. Vickers hardness of the as-cast alloy decreases slightly with a small amount of Sr addition (<0.1 wt%). With the increasing content of Sr (>0.1 wt%), the hardness of the alloys increases first, reaching the peak hardness at 0.6 wt% Sr and then decreases. Moreover, the high temperature treatment would decrease the corresponding hardness for as-cast alloys.