Nanocomposites of reduced graphene oxide (RGO) sheets decorated with amorphous ruthenium oxide nanoparticles are fabricated through a one-pot hydrothermal process without additional dispersants. During the hydrothermal reduction, unilamellar graphene sheets with curved and veil-like morphology are formed and multilamellar graphene sheets are further separated by amorphous RuO₂·xH₂O with a particle size of 3–8 nm. The nanocomposites exhibit evident pseudo capacitance behavior and the comprehensive electrochemical performance is improved markedly compared with that of the single components. When the precursor ratio of graphene oxide (GO) to RuCl₃·xH₂O is 2 : 10, the graphene–RuO₂ (GR) nanocomposite electrode achieves the highest specific capacitance of 542.5 F g⁻¹ and the minimum ESR value of 1.21 Ω at 0.1 A g⁻¹, retaining 94% after 1000 cycles at 1 A g⁻¹. Thus graphene sheets/ruthenium oxide nanocomposites bode well for a promising candidate in supercapacitor technology.