Effects of Si and Cr additions and aging treatment on the stress corrosion cracking(SCC) resistance of Al-Zn-Mg-Cu cast alloys were investigated by C-ring test and electrical conductivity measurement. The SCC resistance of Al-Zn-Mg-Cu cast alloys decreased in the order of Cr containing alloy, Si containing alloy and base alloy. The lowest electrical conductivity of Cr containing alloy exhibited the best SCC resistance and this is probably due to an improved corrosion resistance by forming a passive film on the surface. The over-aged alloys showed the better SCC resistance. This is due to the increased distance between coarse particles at grain boundary. The fracture mode of the alloy was confirmed as intergranular type and showed brittle fracture surface. The SCC mechanism of Al-Zn-Mg-Cu cast alloys was found to be the anodic dissolution model.