Abstract: The microstructure and mechanical properties of Mg-Al alloys with aluminum contents below 3wt% were studied by means of optical microscopy, scanning electron microscopy, X-ray energy dispersive analysis, X-ray diffraction and tensile testing machine. The results show that the microstructure of as-cast Mg-Al alloys with low Al content was composed of α-Mg and β-Mg17Al12 phases. The α-Mg solid-solution was equiaxed dendrite. With the increase of Al content, the size of α-Mg dendrites with a six-fold symmetrical rosette decreased, and the branch became dispersed. Mechanical properties increased basically with the increase of Al content. The tensile strength, yield strength and elongation of the alloy with 2.6wt%Al were 178.8 MP, 62.3 MPa and 11.3%, respectively.