An electromagnetic vibration was generated by simultaneously imposing a strong sta-tic magnetic field (up to 10 T) and an alternative electricity current to the metal.Its effects on the solidification structure of eutectic A1-Si alloy have been investigated experimentally. It is found that the eutectic structure has been refined by solely imposing high magnetic field while it is coarsened under the electromagnetic vibra-tion. Furthermore, polyhedral Si grains and non-dendritic a-A1 appeared when the electromagnetic vibration strength was strong enough. The refining of eutectic struc-ture is attributed to the decrease of diffusion coefficient caused by the strong magnetic field. The coarseness of eutectic structure may be attributed to the convection caused by electromagnetic vibration. Strong convection may break co-operative growth of eutectic phases to form polyhedral Si grains and non-dendritic α-A1.