This study uses commercialized cast iron materials such as FC 250 flake graphite cast iron and FCD 450 spheroidal graphite cast iron as the substrate; then pre-oxidized at 750 °C, 850 °C and 900 °C to obtain the surface scales. The static and dynamic thermal erosion tests were performed on oxidized specimen in order to investigate the effect of the oxide layer of the cast irons on the resistance of the thermal erosion in the molten Al-Si-Cu alloy (ADC12) at 700 °C. The results show that the completeness and adhesion properties of the scales are the important factors that would influence the resistance to the thermal erosion. Since the flake graphite formed interconnected cavities after high temperature oxidized, the suitable sites for the oxide growth, the iron oxide grew faster and penetrated along the flake graphite's boundaries resulting in effective resistance to thermal erosion of ADC12. Therefore, the flake graphite cast iron has greater thermal erosion resistivity than the spheroidal graphite cast iron.