The internal microstructure and other fatigue characteristics of aluminum cast alloy AC2B-T6 with cast skin were investigated. The specimen surface was observed with the plastic replica method using a microscope. The internal microstructure od the alloy with cast skin was found to be different to that with a smooth surface. So the Vickers hardness varied depending on the position of the specimen because of the cooling velocity. In the S-N curve, the fatigue strength scattering of AC2B-T6 with a cast skin was larger than that of AC2A-T6 with a smooth surface. The die cast aluminum allor had a clear fatigue limit, which corresponded to the limit against the fatigue crack initiation.