Mg65+x(Cu0.66Y0.34)30-xZn5 (x=5, 10, 15) alloys and their matrix composites were prepared by water-cooled copper mold casting and water quenching. The microstructures of the bulk samples were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) in order to study the effects of Mg content and cooling rate. The results show that the alloy at x=5 prepared by water-cooled copper mold casting exhibits a fully glass structure. And the alloys at x=10 and 15 are mainly composed of the amorphous phase and Mg solid solution phase, which are amorphous composites. However, the amorphous composite materials prepared by low-cooling-rate water quenching mainly consist of Mg, Mg2Cu, MgZnY and the amorphous phase. The corrosion behavior of the alloys was studied in NaCl neutral solution. The results show that the precipitation of the crystal phase is increased with the increase of the Mg content, but at the same time the decrease of the corrosion resistance occurs. Furthermore, with the same composition, the samples prepared by water cooled copper mold casting at a high cooling rate have the best corrosion resistance while the samples prepared by water quenching at a low cooling rate have the worst.