Abstract: The semisolid slurry of A356 alloy, which is grain-refined by Al-La master alloy, is manufactured by low superheat pouring. The effects of La addition on the morphology and the size of the primary α phase in the semisolid A356 alloy are investigated. The results indicate that semisolid A356 alloy contained certain La addition with particle -like and rosette -like primary α phase can be prepared by low superheat pouring. The size and morphology of primary α phase in the semisolid A356 alloy are markedly improved by La addition. The refining mechanism of La of the primary α phase in semisolid A356 alloy is concerned with the eutectic reaction induced by La in the alloy.