High-energy ball milling and low temperature sintering were successfully employed to fabricate a metal matrix composite of Al reinforced with $Al_2O_3$ particulate. Nano- and/or submicro-sized $SiO_2$ particles embedded in an Al-Mg matrix particle can be obtained by high-energy ball milling. No new phases were found in the high-energy ball milled $Al-0.4;wt.\%Mg-14;wt.\%SiO_2$ powder. Milling of the $Al-Mg-SiO_2$ powder increased the sintering rate and decreased the sintering temperature. The hardness of the sintered $Al-Mg-SiO_2$ composite using the ball-milled powder was about twice that of a sintered composite using a mixed powder due to the fine and homogeneous distribution of $Al_2O_3$ particles formed by the displacement reaction between Al and $SiO_2$ during sintering.