A method for fabricating a magnesium-based alloy includes the steps of: (a) mixing a number of carbon nanotubes with a number of magnesium particles; (b) heating the mixture in a protective gas to achieve a semi-solid-state paste; (c) stirring the semi-solid-paste using an electromagnetic stirring force to disperse the carbon nanotubes into the paste; (d) injecting the semi-solid-state paste into a die; and (e) cooling the semi-solid-state paste to achieve a magnesium-based alloy. An apparatus for fabricating the magnesium-based alloy includes a transferring device, a thixomolding machine, and an electromagnetic stirring device. The transferring device includes a feed inlet. The thixomolding machine includes a heating barrel having two ends, a nozzle disposed at a first end thereof, and an material input positioned at a second end thereof. The electromagnetic stirring device includes an electromagnetic induction coil disposed on an outer wall of the heating barrel.