A hybrid material consisting of cobaltosic oxide (Co3O4) nanocrystals grown on nitrogen-doped graphene aerogels (N-GAs), denoted as Co3O4/N-GAs, is fabricated via a simple one-pot hydrothermal process and utilized as a high-performance bi-functional electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The Co3O4/N-GAs hybrid for the ORR displays an outstanding electrocatalytic performance toward the ORR comparable with commercial Pt/C catalyst in an alkaline medium. Furthermore, our proposed hybrid is also highly active for the OER, making it a promising bi-functional catalyst for both ORR and OER. The obviously enhanced catalytic activity is ascribed to the synergistic effect between Co3O4 and N-GAs.