By using high energy ball milling of a mixture of powders, SiC nanometer sized particle included Al-7wt%Si-0.4wt%Mg composite powder can be obtained. The effect of milling on the Al-Si eutectic reaction of the matrix was studied and it was found that the eutectic reaction occurred during milling. High energy ball milling increased the sintering rate of the composite powder due to increasing diffusion rate that was affected by defect density. Due to the finer microstructure and less pore, the hardness of the sintered composite produced by using the mechanically milled nanocomposite powder was significantly higher than that of the sintered composite produced by using the mixed powder. The nanometer and submicrometer sized SiC particles were found in the sintered composite. (C) 2003 Elsevier B.V. All rights reserved.