A series of tensile tests of AZ61 magnesium alloy were conducted using Gleeble-1500 thermal-mechanical material testing system to learn the effect of the test temperatures and strain rates on the mechanical properties of the alloy. It is indicated that the higher the temperature, the lower the ultimate strength and fracture stress, and the larger the plasticity. It is also revealed that the larger the strain rate is, the higher the ultimate strength of the specimens will be, and the larger the plasticity of the specimens will be. The failure mechanism of the material under high temperature was also analyzed based on the fracture observation. It shows that the high temperatures will induce microvoids or microflaws in the material.