A convenient chitosan-assisted hydrothermal and postannealing strategy was successfully developed to fabricate 2D ultrathin MoS2/graphene heterostructures. The resultant heterostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption-desorption. It was found that the ultrathin MoS2 nanosheets were of few-layered structures (3–4 layers) and were well anchored on the large flexible graphene flakes to form heterostructures, which had more uniform mesoporosity and larger surface area than the pristine MoS2. As a result, the obtained MoS2/graphene heterostructure electrode exhibited superior electrochemical lithium-storage performances such as high reversible specific capacity (∼1100mAhg−1), excellent cyclic stability and significantly enhanced rate capability. The prominent electrochemical performance could be attributed to the robust 2D mesoporous heterostructures composed of ultrathin few-layered MoS2 nanosheets and highly conductive graphene as well as the resultant positive synergistic effect between them.