Graphene/metal oxide composites have attracted considerable attention for various applications, such as energy storage, catalysts, and electronics, however, the lack of effective and environmentally friendly fabrication methods for obtaining uniform graphene/metal oxide nanocomposites on a large scale has been one of the main technical barriers to real applications. We have developed a simple, efficient, and environmentally benign approach to the synthesis of reduced graphene oxide (RGO)/metal oxide composites via hydrothermal reaction of graphene oxide and metal powder under mild reaction conditions. For iron oxide as an example, by controlling the ratio of graphene oxide to Fe powder (mGO/mFe), the hydrothermal temperature, and the addition of a mild oxidizing/reducing agent, the valence of Fe in the iron oxide products can be well tuned, i.e., various iron oxide/RGO composites, including RGO/Fe3O4, RGO/Fe3O4/Fe2O3, and RGO/Fe2O3, could be synthesized. RGO/FexOy composites in this study deliver a Li-ion storage capacity of 988.5 mA h g−1 at a current density of 100 mA g−1. After cycling at 500 mA g−1 for 300 cycles, a capacity of 868.4 mA h g−1 can still be maintained (with no capacity decay). When the current density is 2000 mA g−1, the capacity of 657.0 mA h g−1 is still retained, showing superior rate capability. The work described here provides a promising pathway to construct various graphene-based metal oxides as electrode materials for Li-ion batteries.