Additions of grain refiners based on Ca, Ca/Si, Ab(3)Ti and Al(4)X(3) to pure magnesium and AZ31 alloy result in remarkable microstructure refinement. With proper amount of these refiners addition, the grain size in as-cast ingots is one order of magnitude lower than that without refiner addition. Small amount of refiner addition to alloy AZ31 increases both ultimate and yield strength significantly, and the ductility of the alloy is similar to that without refiner addition. Additions of refiner improve the deformation formability of the AZ31 alloy. The extruded and hot rolled specimens (rods or sheets) with refiner addition are crack free and exhibit higher surface quality and mechanical properties than that without refiner addition.