Abstract: Microstructure characteristics of Al-24%Si alloy was studied at the condition of isothermal electromagnetic stirring.Experiment was divided two groups:Stirring and no stirring during cooling course.Isothermal temperature is 577℃ with shearing time up to 40 minutes.Results discover that primary silicon crystal fragmentation and agglomeration occurs simultaneously in the course of stirring.The size of primary silicon phase tends to a constant. Spherical phase appears in the microstructure.