Abstract: AZ80 magnesium alloy composites reinforced with high volume fraction nickel-plated multi-walled carbon nanotubes were fabricated by friction stir processing. The microstructure and mechanical properties of the composites were analyzed. The results show that the microstructure of the composites becomes fine and dense after five passes of friction stir processing. Carbon nanotubes are uniformly distributed in the center of friction stir zone. The microhardness and tensile strength of the composites increases with the carbon nanotubes'contents. When the volume fraction of the carbon nanotubes is 10. 6%,the microhardness and tensile strength of the composites increased by 40% and 41. 1% compared with AZ80 magnesium alloy after friction stir processing, respectively, and increased by 52% and 2. 7% compared with that AZ80 magnesium alloy which has not been friction stir processed,respectively.