Abstract: A method for fabricating a magnetic graphene-based nanocomposite comprises a mixing step: placing a graphene oxide layer, an iron-containing precursor and a microwave-receiving material in a container; and a microwaving step: applying microwave radiation to the graphene oxide layer, the iron-containing precursor and the microwave-receiving material to reduce the graphene oxide layer into the reduced graphene oxide (RGO) layer and decompose the iron-containing precursor into a plurality of iron nanoparticles adhering to at least one surface of the RGO layer, whereby is formed a magnetic graphene-based nanocomposite. Via applying microwave radiation within one minute, a magnetic graphene-based nanocomposite can be fabricated, whereby is greatly decreased the time to fabricate a composite containing graphene oxide and magnetite. Therefore, the method has advantages of high efficiency and simple processes.