Magnesium matrix nanocomposites reinforced with nano-sized SiC particles (n-SiCp) were fabricated by mechanical stirring and high intensity ultrasonic dispersion processing. The dry sliding friction and wear behavior of the magnesium alloy and its nanocomposites were investigated. The results show that the wear resistance of the nanocomposites is higher than that of pure AZ91D alloy due to the nanoparticles reinforced effects. The wear rate increases linearly with the increase of the load for the matrix and its nanocomposites. The wear process of the matrix and the nanocomposites consists of two stages, i.e. running and stable wear stages. The SEM and LSCM analysis results on the worn surface indicate that the main wear mechanism is adhesive wear, abrasive wear and delamination wear. The load has an important effect on the wear mechanism.