Chemically modified graphene and polyaniline (PANI) nanofiber composites were prepared by in situ polymerization of aniline monomer in the presence of graphene oxide under acid conditions. The obtained graphene oxide/PANI composites with different mass ratios were reduced to graphene using hydrazine followed by reoxidation and reprotonation of the reduced PANI to give the graphene/PANI nanocomposites. The morphology, composition, and electronic structure of the composites together with pure polyaniline fibers (PANI-F), graphene oxide (GO), and graphene (GR) were characterized using X-ray diffraction (XRD), solid-state 13C NMR, FT-IR, scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). It was found that the chemically modified graphene and the PANI nanofibers formed a uniform nanocomposite with the PANI fibers absorbed on the graphene surface and/or filled between the graphene sheets. Such uniform structur...