Al2O3/Al composites were produced by immersing the sintered silica preform in molten aluminum which contained magnesium as impurity. Three distinct regions existed in the penetration behavior of molten me-tal with changing the reaction temperature. These regions are denoted as low temperature regime(75$0^{circ}C$-85$0^{circ}C$) intermediate regime(90$0^{circ}C$-95$0^{circ}C$) and high temperature regime(100$0^{circ}C$$leq$) In the low temperature regime the penetration speed of molten aluminum increased with increasing reaction temperature whereas it decreased in the intermediate regime due to the phase transition of alumina formed by displacement reac-tion. In the high temperature regime the penetration speed of molten aluminum was the highest at 100$0^{circ}C$ which was 3.6 mm/hr But above 105$0^{circ}C$ molten aluminum did not penetrate into the silica preform because of the formation of a dense spinel layer at the preform surface by magnesium in molten Al