Abstract: Grain refinement of AZ91D alloy with intensive melt shearing and its effect on partially remelted semi-solid microstructure were studied. The results showed that the intensive melt shearing prior to solidification has a significant grain refining effect on AZ91D alloy, which can reduce the grain size of ingots cast at 650°C from 500 μm to 170 μm and further to 60 μm when the melt is treated at lower temperature. The initial microstructure plays a very important role on the formation of partially remelted semi-solid structure. The grain refinement achieved by the intensive melt shearing can be remained after partial remelting. Under identical reheating conditions, the uniform and fine microstructure can result in higher effective liquid fraction and more spherical microstructure.