Abstract: Mg-7Zn-0.3La magnesium alloy was prepared by permanent mold casting. The microstructure and mechanical properties of the alloy after heat-treated conditions were investigated by means of optical microscope, scanning electron microscopy and mechanical tests. The results show that the alloy has better microstructure after solution at 335 ℃ for 24 h, and the tensile strength, elongation and micro-hardness of the alloy are 234 MPa, 6.15% and 69.8 HV, respectively. On the basis, the alloy obtains peak aging at 160 ℃ for 25 h, and the short rod and granular precipitates are precipitated on the grain boundary, and fine granular precipitates are precipitated inside the grain. The tensile strength, elongation and micro-hardness of the alloy are 277 MPa, 4.13% and 93.5 HV, respectively.