In order to investigate the variation of solidification structure due to the variation of heated model temperature and casting speed, the aluminum alloys which had the diameter to 6mm from 3mm and the composition of 5wt.%Si and 11.6wt.%Si have been fabricated by the horizontal continuous casting process which has a heated mold. As a result of this reasearch, the microstructures have been unidirectional structures parallel to the casting direction, and the secondary dendrite arm spacing and cell spacing decreased according as casting speed increased in all the compositions. In the eutectic composition, the dendrite structure developed in comparision with hypoeutectic composition. Also, it was confirmed that the mushy zone amplitude decreased with the increase of casting speed.