Abstract: The effects of the addition of 0.3wt% calcium, 0.3wt% titanium, and combined addition of 0.3wt% calcium and 0.3wt% titanium respectively on the microstructures and mechanical properties of Mg-12Al-2Sr-0.3Mn magnesium alloy were studied. The results show that the titanium addition improved the plasticity and strength of the magnesium alloy, though Mg17Al12 phase was aggregated and precipitated, resulting in the formation of the second phase with a coarsened microstructure. When added with calcium, the plasticity of the magnesium alloy increased while the strength decreased due to a great number of continuous net-like Mg17Al12 phases precipitated along the grain boundaries. The eutectic phase quantity increased and its microstructures were refined after the combined addition of titanium and calcium, and then the as-cast microstructure of the magnesium alloy became a relatively fine and uniform, resulting in a significant increase of the strength and toughness.