A germanium-graphene nanocomposite material with three-dimensional nanostructures has been synthesized by an efficient one-step, in situ, and aqueous-based method. The electrochemical properties of the germanium-graphene nanocomposite have been evaluated by galvanostatic discharge-charge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Results show that the germanium-graphene nanocomposite has a much more stable cycling performance than that of the pure germanium, with a capacity of about 832 mA h g-1 after 50 cycles. The rate capability is also improved significantly. The superior performance is attributed to the graphene content, which increases the material's conductivity, enlarges the specific surface area, delivers enough sites to allow dispersion of the Ge nanoparticles without excessive agglomeration, and provides void space to buffer the volume change during discharge-charge cycles. © 2013 The Royal Society of Chemistry.