Graphene-Co3O4 composite with a unique sandwich-architecture was successfully synthesized and applied as an efficient electrocatalyst for oxygen evolution reaction. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses confirmed that Co3O4 nanocrystals were homogeneously distributed on both sides of graphene nanosheets. The obtained composite shows enhanced catalytic activities in both alkaline and neutral electrolytes. The onset potential towards the oxygen evolution reaction is 0.406 V (vs. Ag/AgCl) in 1 M KOH solution, and 0.858 V (vs. Ag/AgCl) in neutral phosphate buffer solution (PBS), respectively. The current density of 10 mA/cm(2) has been achieved at the overpotential of 313 mV in 1 M KOH and 498 mV in PBS. The graphene-Co3O4 composite also exhibited an excellent stability in both alkaline and neutral electrolytes. In particular, no obvious current density decay was observed after 10 hours testing in alkaline solution and the morphology of the material was well maintained, which could be ascribed to the synergistic effect of combining Co3O4 and graphene.