Graphene/polyaniline (PANI) nanocomposites were prepared by reducing graphene oxide with hydrazine in the presence of different amounts of polyaniline nanoparticles. In situ cryo-transmission electron microscope (TEM) images of a graphene oxide (GO)/PANI solution revealed that the PANI nanoparticles were anchored on the surface of the GO sheets. During the reduction, the as-adsorbed PANI nanoparticles were sandwiched between layers of graphene sheets. These PANI nanoparticles acted as spacers to create gaps between neighboring graphene sheets, resulting in a higher surface area compared to pure graphene. Graphene/PANI nanocomposites exhibited the high specific surface area of 891 m2/g. Utilizing this composite material, a supercapacitor with a specific capacitance of 257 F/g at a current density of 0.1 A/g has been achieved.