Ultrafine SnO2-containing nanocomposites were synthesized from glucose/SnCl2 acid solution under hydrothermal environment. The content of SnO2 in the nanocomposites could be adjusted by changing the mass ratio of SnCl2 to glucose in the initial solution. The crystalline structure and morphology of the as-synthesized nanocomposites have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results revealed that the nanocomposites were composed of highly dispersing SnO2 nanoparticles with the sizes of only a few nanometers (3–5nm). Electrochemical tests demonstrated that the electrochemical performances were strongly dependent on the content of SnO2 in the nanocomposites. The nanocomposites containing 75wt.% SnO2 exhibited an outstanding reversible capacity of 610mAh/g and high capacity retention after 200 cycles. The extraordinary performance should originate from the very small size of SnO2 nanoparticles and carbon precursor matrix derived from glucose which can confer the ability to accommodate the volume changes and prevent the agglomeration of Sn particles during charge/discharge process.