This study reports the synthesis of graphene oxide (GO)/polyaniline (PANI) nanocomposites with controllable morphologies through in-situ polymerization of aniline monomers in the presence of GO sheets. Specific reaction parameters including solution acidity, aniline concentration, and reaction temperature are used to control the final shape of the composite product. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images are used to explore the morphology of the composite. Thermogravimetric analysis (TGA), X-ray diffraction (XRD). FT-IR and UV-vis spectrophotometers are utilized to characterize the intermediates and the final products of the GO/PANI composites. Experiment results reveal that the polymerization operated in low acidity and low temperature conditions inclines to form GO/PANI nanotubes. On the other hand, the polymerization operated in high acidity inclines to form either nanospheres or aligned nanofiber arrays. These different morphologies are resulted from different polymerization routes and the formation mechanisms of these different shapes of nanocomposites are explored. Among the various nanocomposites, the GO/PANI nanospheres exhibit a highest electrochemical surface area. This study provides a facile and effective strategy to control the morphology of GO/PANI nanocomposites with characteristic electrochemical property. (c) 2012 Elsevier Ltd. All rights reserved.