Three-dimensional reduced graphene oxides hydrogel anchored with ultrafine CoO nanoparticles (CoO/RGO nanocomposite) is prepared by a facile hydrothermal strategy and subsequently heat-treatment process. The small-size CoO nanoparticles are encapsulated within graphene-based hydrogel with robust interconnected networks for the CoO/RGO nanocomposite. The electrochemical performances are evaluated by using coin-type cells. It delivers high rate capacities of 890.2, 690.4, 543.8 and 457.0mAhg−1, even at 200, 800, 1600 and 2400mAg−1, respectively. The specific capacity increases to 1025.8mAhg−1 after 82 cycles when the current density is back to 100mAg−1, indicating excellent rate capability and cycle stability. The improved electrochemical performance is ascribed to the fabricated structure with three-dimensional RGO nanosheets. The CoO/RGO nanocomposite will be a promising candidate of anode material for lithium ion batteries.