Cuprous oxide (Cu2O) sub-microspheres @ reduced graphene oxide (rGO) nanosheets core-shell composites with 3D architecture are successfully fabricated by a one-step method through co-reduction of irregular cupric citrate and graphene oxide nanosheets at room temperature. Comparing to the bare Cu2O sub-microspheres and the simple physical mixture of Cu2O and rGO (Cu2O-rGO-M), the Cu2O@rGO electrodes demonstrate dramatically improved capacity, cyclic stability and rate capability as anode materials for lithium ion batteries. At a low current density of 100 mA∙g−1, Cu2O@rGO electrodes deliver a discharge capacity of 534 mAh∙g−1 after 50 cycles, retaining 94% of the initial capacity. Under a higher current density of 1000 mA∙g−1, Cu2O@rGO electrodes exhibit a discharge capacity of 181 mAh∙g−1 after 200 cycles, approximately 4 times larger than that of bare Cu2O sub-microsphere electrodes. The rate capacity retention of Cu2O@rGO electrode is 74% at 200 mA∙g−1 and 38% at 1000 mA∙g−1 relative to 100 mA∙g−1, much better than that for Cu2O-rGO-M (52% and 34%) and bare Cu2O electrodes (13% and 3%,). The enhanced electrochemical performance for Cu2O@rGO might be ascribed to the rGO coating and 3D architecture. The outer coated rGO nanosheets could provide additional 3D conductive networks as well as serve as the buffer layers for accommodating the large volume change of the inner Cu2O sub-microspheres during the charge-discharge cycling.