Abstract: The influence of low frequency electromagnetic field on ingot surface quality and as-cast microstructure in horizontal direct chill (HDC) casting process were investigated experimentally. The casting surfaces and as-cast microstructures of the ingots by conventional HDC and low frequency electromagnetic HDC casting were compared. The results show that low frequency electromagnetic field can significantly reduce the surface defects and refine the as-cast microstructures. Further more, increasing electromagnetic intensity and decreasing frequency are both beneficial to the improvement of ingot quality. The optimal number of ampere-turns and frequency available to the experiments are found to be 10000 and 30 Hz, respectively.