A 3D graphene architecture can be prepared via an in situ self-assembly of graphene prepared by a mild chemical reduction. Fe(3)O(4) nanoparticles are homogeneously dispersed into a graphene oxide (GO) aqueous suspension, and a 3D magnetic graphene/Fe(3)O(4) aerogel is prepared during the reduction of GO to graphene. This provides a general method to prepare 3D graphene/nanoparticle composites for a wide range of applications including catalysis and energy conversion.